Question 584607
Let {{{a}}} = cost/pound of cinnamon tea 
Let {{{b}}} = cost/pound of spice tea 
(1) {{{ 8a + 4b = 38 }}}
and
(2) {{{ 10a + 12b  = 72 }}}
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Multiply both sides of (1)  by {{{3}}} 
and subtract (2) from (1)
(1) {{{ 24a + 12b = 114 }}}
(2) {{{ -10a - 12b = -72 }}}
{{{ 14a = 42 }}}
{{{ a = 3 }}}
and
(1) {{{ 8*3 + 4b = 38 }}}
(1) {{{ 24 + 4b = 38 }}}
(1) {{{ 4b = 14 }}}
(1) {{{ b = 3.5 }}}
The cost/pound of cinnamon tea is $3 
The cost/pound of spice tea is $3.50
check:
(2) {{{ 10*3 + 12*3.5  = 72 }}} 
(2) {{{ 30 + 42 = 72 }}}
(2) {{{ 72 = 72 }}}
OK