Question 1012471
Let {{{ a }}} = the price of a can of house paint
Let {{{ b }}} = the price of a can of wall paint
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(1) {{{ a = b + 4 }}}
(2) {{{ 7a  = 9b }}}
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Substitute (1) into (2)
(2) {{{ 7*( b + 4 )  = 9b }}}
(2) {{{ 7b + 28 = 9b }}}
(2) {{{ 2b = 28 }}}
(2) {{{ b = 14 }}}
and
(1) {{{ a = b + 4 }}}
(1) {{{ a = 14 + 4 }}}
(1) {{{ a = 18 }}}
The price of a can of house paint is $18
The price of a can of wall paint is $14
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check:
(2) {{{ 7a  = 9b }}}
(2) {{{ 7*18  = 9*14 }}}
(2) {{{ 126 = 126 }}}
OK