Question 410761
Let {{{a}}} = cost per case of juice
Let {{{b}}} = cost per case of bottled water
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In words:
(cost per case) x (a certain number of cases) = cost for that many  cases
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given: 
(1) {{{6a + 1b = 135}}}
(2) {{{4a + 2b = 110}}}
Multiply both sides of (1) by {{{2}}}
and subtract (2) from (1)
(1) {{{12a + 2b = 270}}}
(2) {{{-4a - 2b = -110}}}
{{{8a = 160}}}
{{{a = 20}}}
and, since
(1) {{{6a + 1b = 135}}}
{{{6*20 + b = 135}}}
{{{b = 135 - 120}}}
{{{b = 15}}}
$20 is the cost per case of juice
$15 is the cost per case of bottled water
check answer:
(2) {{{4a + 2b = 110}}}
(2) {{{4*20 + 2*15 = 110}}}
{{{80 + 30 = 110}}}
{{{110 = 110}}}