Just think of it as normal subtraction. They both have the same denominators all you need to do is subtract. 11/12-7/12 is 4/12 if you simplify which just means to find the number that both 4 and 12 can go into equally the simplified answer would be 1/3. You just need to divide 4 by both the top and the bottom (numerator and denominator).
39/40 as a decimal is 0.975
When you divide by the reciprocal, you flip the numbers and multiply across.
