The lifetime of a machine part has a continuous distribution on the interval (0, 40) with probability density function ƒ, where ƒ(x) is proportional to (10 + x)^-2. Calculate the probability that the lifetime of the machine part is less than 6. Choose one of the following.

(a) 0.04 

(b) 0.15 

(c) 0.47 

(d) 0.53 

(e) 0.94