Question 1064757
Let {{{ a }}} = Joe's age now
Let {{{ b }}} = his father's age now
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(1) {{{ b = 4a }}}
(2) {{{ b + 6 = 3*( a + 6 ) }}}
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(2) {{{ b + 6 = 3a + 18 }}}
(2) {{{ -3a + b = 12 }}}
Substitute (1) into (2)
(2) {{{ -3a + 4a = 12 }}}
(2) {{{ a = 12 }}}
and
(1) {{{ b = 4a }}}
(1) {{{ b = 4*12 }}}
(1) {{{ b = 48 }}}
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Joe is 12
His father is 48