Create 20. function: add & subtract times

//write function add_times -takes 2 variables of type MyTime as input args &
//outputs a return value which is sum of the 2 times + outputs should be in
//'canonical form' (0<=t.seconds<60 / 0<=t.minutes<60 / 0<=t.hours
//function prototype should look like MyTime add_time(MyTime t1, Mytime t2);
//write analogous subtract_times function