Question 490747
The simple, direct way is to call the 3 parts
{{{a}}}, {{{b}}}, and {{{c}}}
given:
(1) {{{ a + b + c = 72 }}}
(2) {{{ a = b - 3 }}}
(3) {{{ c = b/2 }}}
-------------
Now substitute (2) and (3) into (1)
(1) {{{ b - 3 + b + b/2 = 72 }}}
Multiply both sides by {{{2}}}
(1) {{{ 2b - 6 + 2b + b = 144 }}}
(1) {{{ 5b = 150 }}}
(1) {{{ b = 30 }}}
and, since
(2) {{{ a = b - 3 }}}
(2) {{{ a = 30 - 3 }}}
(2) {{{ a = 27 }}}
and
(3) {{{ c = b/2 }}}
(3) {{{ c = 15 }}}
The parts are 27, 30 and 15