there is a normal distribution with a mean of 13 and standard deviation of 36. Find a value with a z-score of -1.69

Diana is painting statues she has 7/8 of a liter of paint each statue requires 1/20 of a liter of paint how many statues can she paint?

We just started the introduction into circles and i have no idea how to do this.

Can someone factor this fully? my friend and i have two different answers and i would like to know if either of them is right. you in advance. a^2 - b^2 + 25 + 10a