What is the inverse of the function f(x) =2x +1

This one is a bit confusing but I'll try to answer. Since the sum is given and one of the addend is given, we need to perform subtraction to get the other addend.

     8d⁵ - 3c³d² + 5c²d³ - 4cd⁴ + 9  ⇒ SUM
-    2d⁵ -   c³d²              + 8cd⁴ + 1  ⇒ 1ST ADDEND
     6d⁵ - 2c³d² + 5c²d³ -12cd⁴ - 8 ⇒ 2ND ADDEND