From the problem
you can get the equation
4(30+0.20x) < 300
the 4 represents that it is within 4 days, the 30 is the daily fee, the 0.20 is the rate of per mile driven per day, and the 300 is how much money you have left to spend.
now we solve for x, first distribute the 4 into the parenthesis
120 + 0.80x < 300 then subtract 120 from both sides
-120 -120
and get 0.80x < 180 then divide both sides by 0.80
/0.80 /0.80
therefore x = 225
so you can drive 225 miles.