A is directly proportional to B^2 . When B=6, A=54 . Write a formula relating A and B, and find A when B= 13.

Immediately a general formula can be written:A = kB²where k is a constant to be found . This can be rearranged to make k the subject; k can then be found using the values of A and B given:k = A/(B²) = 54/6² = 3/2 . The general formula can then be written in its final form:A = 3/2B²B=13 can then be put into the formula above to give A = 253.5