Question 547239
(1) {{{ 7r - 3s = 3 }}}
(2) {{{ 3r + 7s = 51 }}}
Multiply both sides of (1) by {{{7}}}
Multiply both sides of (2) by {{{3}}}
Then add the equations
(1) {{{ 49r - 21s = 21 }}}
(2) {{{ 9r + 21s = 153 }}}
{{{ 58r = 174 }}}
{{{ r = 3 }}}
and, since
(1) {{{ 7r - 3s = 3 }}}
(1) {{{ 7*3 - 3s = 3 }}}
(1) {{{ 3s = 21 - 3 }}}
(1) {{{ 3s = 18 }}}
(1) {{{ s = 6 }}}
Check answers:
(2) {{{ 3r + 7s = 51 }}}
(2) {{{ 3*3 + 7*6 = 51 }}}
(2) {{{ 9 + 42 = 51 }}}
(2) {{{ 51 = 51 }}}
OK