Okay so you basically assume f(x) is 0.
The positive quadratic formula (as a refresher) is x= (-b+√b∧2-4ac)/2a
By looking at the equation you can determine
a=1
b=2.6
c=-7.32
And plug these in to solve
-2.6+√6.76+7.32)/2
Once you solve the answer will be x=1.7