Question 186343
Let {{{m}}} = number of main floor tickets sold
Let {{{u}}} = number of upper level tickets sold
given:
(1) {{{m + u = 50000}}}
(2) {{{25m + 12u = 1112000}}}
There are 2 equations and 2 unknowns. When the 
number of equations matches the number of unknowns,
it is solvable.
Multiply both sides of (1) by {{{12}}}
and subtract from (2)
(2) {{{25m + 12u = 1112000}}}
(1) {{{-12m - 12u = -600000}}}
(3) {{{13m = 512000}}}
(3) {{{m = 39385}}} (rounded off)
and
(1) {{{m + u = 50000}}}
(1) {{{39385 + u = 50000}}}
(1) {{{u = 10615}}} (rounded off)
39,385 mainfloor seats were sold and 10615 upper level 
seats were sold
check answer:
(2) {{{25m + 12u = 1112000}}}
(2) {{{25*39385 + 12*10615 = 1112000}}}
(2) {{{984625 + 127380 = 1112000}}}
(2) {{{1112005 = 1112000}}} (close enough)
and
(1) {{{m + u = 50000}}}
(1) {{{39385 + 10615 = 50000}}}
(1) {{{50000 = 50000}}}
OK