Answer: If P(x<a) = 0.6, then the value of a will be 0.25.
In this type of problem, it is safe to assume the normal distribution unless you are told something different.
In this probability, we have to find the z-score for a that gives a probability of 0.6. You will need a normal distribution chart to do this problem. Just find the probability that is closest to 0.6 and use that z-score.