7. The school organizes 1511 people to go on an outing, renting 42-seat coaches and 25-seat minibuses. If it is required that there is exactly one seat per person and one person per seat, then there are $\qquad$ rental options.
【Key Point】Indeterminate Equation
【Answer】2
【Analysis】Let $a$ be the number of large buses, and $b$ be the number of medium buses.
According to the problem, set up the indeterminate equation $42 a+25 b=1511$
$1511 \div 25 \cdots 11$, then $42 a \div 25 \cdots 11, 42 a$ ends in 6, by trial when $a=8$, $b=47$; when $a=8+25=33$, $b=5$, there are 2 sets of integer solutions.