add and subtract time

How do I add and subtract hours minutes and seconds?

I知 writing a program to find when the sun is directly overhead. I知 doing this so that I can find the true north/south line. In the example on my program, at the town of Farmington, a plumb bob will cast a shadow on the north/south line at 11:51:39 on June 16

Can somebody help me with the holes in my program? I知 almost there
(EoT sheet 2)