Trigonometry questions

Hii1977 cleaner shrimp are a species of shrimp that clean parasites from other organisms. fish allow the shrimp to eat the parasites in their mouth. the shrimp get a source of nutrition. the relationship between the shrimp and the fish is this association indicates that for the smaill aneser arecommensal,mutualistic,or parasitic for the begger one the anser are the shrimp and fish benefit each other , the shrimp harm the fish, or the fish do not benetit from the shrimp

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

Can someone me with my math problem pls my teacher is on my back about this