probability – the life in hours of a certain part of radio tube is a continuous random variable X with p.d.f. given by:f(x)={100/x2,x≥100 and 0,otherwise

Suppose that the life in hours of a certain part of the radio tube is a continuous random variable X with p.d.f. given by:f(x)={100/x2,x≥100 and 0,otherwise
What is the probability that a tube will last less than 200 hours if it is known that the tube is still functioning after 150 hours of service?