P(1) is the probability that the machine needs replacent after 1 year

P(2) is the probability that the machine needs replacent after 2 years

etc.

So the probability that the machine needs to be replaces in 3 or fewer years is P(1)+P(2)+P(3)=0.7

So the probability that the machine needs no replacement in 3 years is 1 minus the probability that it needs replacement in 3 or less years.

CB