Answer:
step by step!
Explanation:
let it be know, that ALL triangles equal up to 180 degrees. we know that triangle a has a 90 degree angle. first lets find the missing angle (purple question mark in triangle a): 25 + 90 = 115. 180 - 115 = 65.
you also know that the blue line is 180 degrees, so you can use the given measurement, 75, and the on you just found, 65, to find the last one. 65 + 75 = 140. 180 - 140 = 40 (purple question mark in triangle b).
now looking at triangle b, the given measurement, 40, and the one you just found, also 40, PLUS the ?, will equal 180. to do this you will do 40 + 40 = 80. 180 - 80 = 100.
? equals to 100 degrees.