For this case we have the following quadratic functions:
Revenue: 
Cost: 
Then, we observe that the profit is given by the following mathematical relationship:

Substituting values we have:

Making the corresponding calculations we have:

Answer:
An expression that represents the profit is:

Answer:
k
2
+
k
+
1
Step By Step:
Cancel the common factor.
Then.
k
2
+
k
+1
by 1
Gets you k2+k+1