In the given equations, the function of \(\bigstar\) remains unchanged. What number will come in place of question mark (?) in the fourth equation?

I. \(4 \ \bigstar \ 3 = 15\) 

II. \(7 \ \bigstar \ 3 = 24\)

III. \(6 \ \bigstar \ 5 = 33\)

IV. \(9 \ \bigstar \ 2 = ?\)