Again more free points

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

Ineed with the quizzes in apex mathematics ii

Acafeteria manager can choose from among six side dishes for the lunch menu: applesauce, broccoli, corn, dumplings, egg rolls, or french fries. he used a computer program to randomly select three dishes for monday's lunch. what is the theoretical probability the applesauce and broccoli will both be offered monday?