Write and solve an inequality:
Total(t) = $5.42 + ($1.08/therm)(t) ≤ $87.50.
First, subtract $5.42 from $87.50: then ($1.08/therm)(t) ≤ $82.08
Next, divide both sides by $1.08 per therm:
t ≤ ($82.08) / ($1.08/therm) = 76 therms (maximum). Thus, Rameen's usage could be [0,76] (therms).