Question 577267
These are 2 straight lines and the solution
is their intersection. Since 2 straight lines
can only intersect at 1 point, there is only
1 solution.
------------
Get both lines into the standard form:
(1) {{{ x = 7 - 2y }}}
(1) {{{ x + 2y = 7 }}}
and
(2) {{{ y = 3x }}}
(2) {{{ 3x - y = 0 }}}
----------------
Now multiply both sides of (2) by {{{ 2 }}},
and add the equations
(1) {{{ x + 2y = 7 }}}
(2) {{{ 6x -2y = 0 }}}  
{{{ 7x = 7 }}}
{{{ x = 1 }}}
Now plug this value back into either (1) or (2)
(2) {{{ 3*1 - y = 0 }}}
(2) {{{ -y = -3 }}}
(2) {{{ y = 3 }}}
The solution is (1,3)
Here's a plot of the lines:
{{{ graph( 400, 400, -10, 10, -10, 10, 3x, -(1/2)*x + 7/2 ) }}}