Question 1053195
(1) {{{ k = j + 5 }}}
(2) {{{ m = 3k }}}
(3) {{{ k + j + m = 40 }}}
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(1) {{{ j = k - 5 }}}
Substitute (1) and (2) into (3)
(3) {{{ k + k - 5 + 3k = 40 }}}
(3) {{{ 5k - 5 = 40 }}}
(3) {{{ 5k = 45 }}}
(3) {{{ k = 9 }}}
and
(1) {{{ j = k - 5 }}}
(1) {{{ j = 9 - 5 }}}
(1) {{{ j = 4 }}}
and
(2) {{{ m = 3k }}}
(2) {{{ m = 3*9 }}}
(2) {{{ m = 27 }}}
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Kevin is 9
Jack is 4 
Mike is 27
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check:
(1) {{{ k = j + 5 }}}
(1) {{{ 9 = 4 + 5 }}}
(1) {{{ 9 = 9 }}}
OK
You can check (2) and (3)