Question 561152
Let {{{ a }}} = charge / month for microfiber couch
Let {{{ b }}} = charge / month for leather couch
given:
(1) {{{  b = a + 30 }}}
(2) {{{ 12a + 8b = 1620 }}}
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Substitute (1) into 2)
(2) {{{ 12a + 8*( a + 30 ) = 1620 }}}
(2) {{{ 12a + 8a + 240 = 1620 }}}
(2) {{{ 20a = 1620 - 240 }}}
(2) {{{ 20a = 1380 }}}
(2) {{{ a = 69 }}}
and
(1) {{{  b = a + 30 }}}
(1) {{{ b = 69 + 30 }}}
(1) {{{ b = 99 }}}
$69 / month for microfiber couch
$99 / month for leather couch
check:
(2) {{{ 12*69 + 8*99 = 1620 }}}
(2) {{{ 828 + 792 = 1620 }}}
(2) {{{ 1620 = 1620 }}}
OK