Answer:
The equation involving three variable and one constant is
a b - c = 9
Adding , c on both sides
→ a b - c + c = 9 +c
→ a b = 9 + c
Subtracting ,9 from both sides
→a b -9 = 9 +c -9
→a b - 9 = c + 9-9→ [ Used associative property of addition, (a + b)+c=b +(a+c)]
→ a b -9 =c
c= a b - 9