Technically, the car on the right has the right-of-way in an unmarked intersection: https://app.leg.wa.gov/RCW/default.aspx?cite=46.61.180

This law is valid even if it’s a “T” intersection, where one might assume that going “straight” has the right-of-way over the person turning. Juries have been advised the following from Jury Instruction 70.02:
The right of way is not absolute, however, and there are some exceptions. The exceptions include to act reasonably under the circumstances. If you clearly see that the car on the left is not going to stop, you have an obligation to act reasonably and avoid the car accident.

Several 41.5 intersections are unmarked (no stop signs), such as:

• 171st Ave SE/SE 40th PL
• 172nd PL SE/SE 40th PL
• 173rd PL SE/SE 40th PL

Cars travelling East on SE 40th PL technically have to yield to the cross streets above if they approach the intersection at the same time. Residents might assume that SE 40th PL is classified as an “arterial” (see #2 modifier below in RCW 46.61.180). WSDOT has a map classifying what’s considered an “arterial” and SE 40th PL is NOT considered an arterial (green = minor arterial, purple= major collector):

From RCW link:
RCW 46.61.180

Vehicle approaching intersection—Vulnerable users of a public way—Fine. (Effective January 1, 2020.)

(1) When two vehicles approach or enter an intersection from different highways at approximately the same time, the driver of the vehicle on the left shall yield the right-of-way to the vehicle on the right.
(2) The right-of-way rule declared in subsection (1) of this section is modified at arterial highways and otherwise as stated in this chapter.
(3)(a) When the vehicle on the right approaching the intersection is a vulnerable user of a public way, a driver of a motor vehicle found to be in violation of this section must be assessed an additional fine equal to the base penalty assessed under RCW 46.63.110(3). This fine may not be waived, reduced, or suspended, unless the court finds the offender to be indigent, and is not subject to the additional fees and assessments that the base penalty for this violation is subject to under RCW 2.68.040, 3.62.090, and 46.63.110.
(b) For the purposes of this section, "vulnerable user of a public way" has the same meaning as provided in RCW 46.61.526(11)(c).
(4) The additional fine imposed under subsection (3) of this section must be deposited into the vulnerable roadway user education account created in RCW 46.61.145.