Question 934798
Let {{{ a }}} = number of adult tickets sold
Let {{{ s }}} = number of student tickets sold
--------------
(1) {{{ a + s = 553 }}}
(2) {{{ s = a + 53 }}}
------------------
Substitute (2) into (1)
(1) {{{ a + a + 53 = 553 }}}
(1) {{{ 2a = 553 - 53 }}}
(1) {{{ 2a = 500 }}}
(1) {{{ a = 250 }}}
250 adult tickets were sold