So for this you just want to divide 4/5 by 9/10 because it is the opposite of the equation.
9/10 / 4/5
To divide fractions, you just multiply and reverse the second fraction.
For example:
9/10 * 5/4
Now you can just normally multiply.
45/40
Or, simplified,
9/8
(Or 1 1/8)
