It appears the first two digits in the code is the two digits out front multiplied together. The next digit or two are the sum of the two numbers. The last number or two is the difference.
7x3 = 21
7+3 = 10
7-3 = 4
(7)(3) = 21104
It's the same process for the (9)(4) = 36135
So for (8)(5) would be:
8x5=40
8+5=13
8-5=3
(8)(5)= 40133