Multiply the number of days (x) by the amount per day (80) to get 80x.
She is driving 150 miles at 0.10 per mile so multiply to get the mileage cost: 150 x 0.10 = 15
Add this to the daily amount:
80x+15
She can spend up to 300, so less than or equal to 300:
80x +15 <=300