Please help me solve the problem

Probability of getting a green marble=5/15=3/5

Probability of getting a black marble=5/15=3/5

f(x) has value 150 at x= 0

and 0 at x= 3

so d(f(x))/dt = slope = -150/3 = -50

i think that you should ask google for the answer to that problem because if we don't know it google does