y is proportional to x^2 and that when y = 75, x = 5. Find a formula for y in terms of x and find y when x=3

In a proportional equation, you represent the factor of proportionality as k. In this case it means that y=kx^2. In the question you're given a number for both y and x. Sub these in in order to solve for k. This would mean that 75=k(5)^2. This leads to 75=25k. This leads to k=3. The formula for y in terms of x is therefore y=3x^2.Now that you have k you can sub in the value given to you in the question for x in order to find y. This leads you to have y=3(3)^2. y=3(9)y=27.