Question 241880
Let {{{a}}} = units/day of lumber needed
Let {{{b}}} = units/day of plywood needed
given:
(1) {{{b = 3a}}}
(2) {{{30a + 40b = 15600}}}
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Substitute (1) in (2)
(2) {{{30a + 40*(3a) = 15600}}}
{{{30a + 120a = 15600}}}
{{{150a = 15600}}}
{{{a = 104}}}
{{{b = 3a}}}
{{{b = 3*104}}}
{{{b = 312}}}
{{{104}}} = units/day of lumber needed
{{{312}}} = units/day of plywood needed