We are give that the two triangles are proportional, this means that:
BC/EF = CA/FD
We are also given that:
BC = 9 units
EF = 90 units
CA = b (The value we want to calculate)
FD = 360 units
Substitute with the givens in the proportionality relation mentioned above to get the value of b as follows:
BC/EF = CA/FD
9/90 = b/360
b = (9/90) * 360
b = 36 units
