C program to compute the sum of the following series up to nth term (take n as use input): Total = 1 * 3 + 11 * 13 + 21 * 23 + 31* 33 + … How can I solve this?

Estimate the change in specific internal energy au and specific enthalpy h from inlet to outlet for ethylene glycol (a liquid) flowing through each of the following devices: (a) a heat exchanger where the glycol temperature increases from 20 °c to 80 °c; (b) a pump operating at about 25 °c and increasing the glycol pressure from 100 kpa to 8 mpa.