Can someone tell me the formula i would use for this and how to solve through?

Write two subtraction equations that are equivalent to 5 + 12 = 17.

Which of the points a(6, 2), b(0, 0), c(3, 2), d(−12, 8), e(−12, −8) belong to the graph of direct variation y= 2/3 x?

Prove that the value of the expression 7^8–7^7+7^6 is divisible by 43.