Prove that: c)
12^13–12^12+12^11 is divisible by 7 and 19.
d)
11^9–11^8+11^7 is divisible by 3 and 37.
e)
25^9+5^17 is divisible by 30.
f)
27^10–9^14 is divisible by 24.

Two farmers pay a total rent of $140 for a pasture. the first farmer placed $4 oxen in the pasture, and the second farmer placed $30 sheep in the pasture. the farmers split the rent based on the proportion of the pasture eaten by their own animals that month. how much should the first farmer pay, if 1 ox eats as much as 10 sheep in a month?