I need help with this question please

How to choose the sign of the radical in the denominator of the formula for the distance from a point to a line.

Cassie is traveling 675 miles today to visit her brother and his family. so far, she has stopped for gas three times. at the first stop, she put in 7.1 gallons of gas and paid $23.79. at her second stop, she put in 5.8 gallons of gas and paid $19.08. and, at the third stop, 6.6 gallons and paid $20.39. at which stop did casey pay the most for gas?

For f(x)=2x+3 and g(x)=x^2- 8 find (f+g) (x)