Question 613803
Let {{{ d }}} = Denise's age now
Let {{{ c }}} = Cheryl's age now
given:
(1) {{{ d = 2c + 6 }}}
(2) {{{ d + 21 + c + 21 = 99 }}}
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(1) {{{ d - 2c = 6 }}}
and
(2) {{{ d + c = 99 - 42 }}}
(2) {{{ d + c = 57 }}}
Subtract (1) from (2)
(2) {{{ d + c = 57 }}}
(1) {{{ -d + 2c = -6 }}}
{{{ 3c = 51 }}}
{{{ c = 17 }}}
and, since
{{{ d = 2c + 6 }}}
{{{ d = 2*17 + 6 }}}
{{{ d = 40 }}}
Cheryl is 17 now