First, the relationship between B, bookings and R, rate is linear
the slope of that relationship is (100-95)/(300-350)=-1/10
The equation for the relationship is -1/10 = (B-95)/(R-350) => B=(1300-R)/10
Revenue = BR = (1300R - R2)/10
The maximum occurs where (1300 - 2R) = 0 => R = 650
At that rate the hotel will book 65 guests and revenue will be 42900