1. Change your Euler method program (see the previous assignment) to make it the Modified Euler method.
   Then use it to solve the same sample problem we solved in class using a stepsize of h = 0.2.

2. Change your program to make it the Classical Runge–Kutta method.
   Then use it to solve the same sample problem we solved in class using a stepsize of h = 0.2.

3. Change your program to make it the Runge–Kutta–Fehlberg method.
   In this case also estimate the error at each node.
   Then use the program to solve the same sample problem we solved in class using a stepsize of h = 0.2.