For the sake of ease, let's change 36 into a fraction.
36/1 * 4/9
Now, multiply the numerators together to get the product's numerator and the denominators together to get the product's denominator.
36 * 4 = 144
1 * 9 =
144/9
Now simplify...
144/9 = 16
There's your answer!
36 * 4/9 = 16