Question 1031377
Let {{{ s }}} = Sally's age now
Let {{{ f }}} = Fred's age now
------------------------
(1) {{{ s = 2f }}}
(2) {{{ s - 4 = 3*( f - 4 ) }}}
------------------------
(2) {{{ s - 4 = 3f - 12 }}}
(2) {{{ 3f = s + 8 }}}
Plug (1) into (2)
(2) {{{ 3f = 2f + 8 }}}
(2) {{{ f = 8 }}}
and
(1) {{{ s = 2f }}}
(1) {{{ s = 2*8 }}}
(1) {{{ s = 16 }}}
---------------------
Sally is 16 and Fred is 8
---------------------
check:
(2) {{{ s - 4 = 3*( f - 4 ) }}}
(2) {{{ 16 - 4 = 3*( 8 - 4 ) }}}
(2) {{{ 12 = 3*4 }}}
(2) {{{ 12 = 12 }}}
OK