You simply MUST learn to manipulate "Basic Principles".
i = 0.06
m = i/12 = 0.06/12 = 0.005
a = 1+m = 1.005
P is the desired payment.
Now think about the 36 payments. The first will be credited interrest 36 times. The last only once. This gives.
Can you add up the Geometric Sequence in the parentheses?