Calculate the efficiency of a light bulb if it produces 30J of light energy, while 95J of electrical energy are input

F(x) = 3x - 5;   x = 2, x = 3

[f(3) - f(2)/ (3 - 2)

f(3) = 3x - 5                            f(2) = 3x - 5
f(3) = 3(3) - 5                         f(2) = 3(2) - 5
f(3) = 9 - 5                              f(2) = 6 - 5
f(3) = 4                                   f(2) = 1

average rate of change; 

(4 - 1)/(3 - 2) = 3

hope this helped, God bless!