The steepest graph is gonna be the one with the largest slope.
in y = mx + b form, the slope is in the m position...
y = 3x - 16....slope is 3
y = 2x + 7/15....slope is 2
y = x + 24....slope is 1
y = 1/2x + 3.....slope is 1/2
so y = 3x - 16 will have the steepest slope because it has the largest slope