Bear in mind that multiplying anything, and anything whatsoever by 1, has a product of the anything itself.
so, let's multiply 2/3 by 1 then and check about,
90. The measure of an inscribed angle is half of that of the measure of its arc, and the measure of the angle corresponding with arc a is 45. 45*2 is 90, so 90 is the measure of arc a.