Question related to PERT

Please help me by answering this question and technique to be followed.

Using PERT calculation the variance of the project is found to be 25 days. What is the range of the values for the project duration such that there will be about 95% probability that the actual project completion will fall in between the high and low value of the range of values.?

a) 164 - 174 days

b) 154 - 184 days

c) 119 - 219 days

d) 159 - 179 days

Be careful on these kinds of question. - Doug Battista