Question 552775
Let {{{ b }}} = Brad's age now
Let {{{ f }}} = Father's age now
{{{ b + 4 }}} = Brad's age in 4 years
{{{ f + 4 }}} = Father's age in 4 years
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given:
(1) {{{ b + f = 58 }}}
(2) {{{ f + 4 = 2*( b + 4 ) }}}
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(1) {{{ b = 58 - f }}}
Substitute (1) into (2)
(2) {{{ f + 4 = 2*( 58 - f + 4 ) }}}
(2) {{{ f + 4 = 116 - 2f + 8 }}}
(2) {{{ 3f = 116 + 8 - 4 }}}
(2) {{{ 3f = 120 }}}
(2) {{{ f = 40 }}}
and, since
(1) {{{ b + f = 58 }}}
(1) {{{ b + 40 = 58 }}}
(1) {{{ b = 18 }}}
Brad is 18 and Father is 40 
check answer:
(2) {{{ f + 4 = 2*( b + 4 ) }}}
(2) {{{ 40 + 4 = 2*( 18 + 4 ) }}}
(2) {{{ 44 = 2*22 }}}
(2) {{{ 44 = 44 }}}
OK