I need help on this assignment I’m very low in my class rn and this will raise it up HELP ‼️

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

If you were constructing a triangular frame, and you had wood in the length of 4inches, 4 inches, and 7 inches, would it make a triangle? would you be able to create a frame from these pieces of wood?

Quickly multiply and simplify polynomials (x – 4) (x^2 – 5x – 6)