The total cost for X hours is the fixed cost of $15 plus the variable cost of $4 per hour which is equal to 4*X, so the total cost is 4*X + 15
If Margie does not want to spend more than $27 then the inequality is
4*X + 15 <= 27
4*X <= 12
X <= 3
If Margie does not want to spend more than $27 then she cannot rent the bicycle for more than 3 hours