Expand the left hand side:
[tex]17f+34+45.99<200[/tex]
Simplify the left hand side:
[tex]17f+79.99<200[/tex]
Subtract 79.99 from both side:
[tex]17f<120.01[/tex]
Divide both sides by 17:
[tex]f<\dfrac{120.01}{17} \approx 7.06[/tex]
So, he must invite less than 7 friend to the party.