We're supposed to put the correct answer in each box? Thanks for clarifying.
What a contrived question. We plot.
Rejecting the negative solution we see intersection at x=7.
[tex]S=2^7 + 12 = 128+12 = 140 [/tex]
[tex]S = 15(7)+35 = 20(7)=140 \quad\checkmark[/tex]
First Answer Box: 7
Second Answer Box: 140
