Question 2754
this {{{x = (7 -5y)/4}}} is correct, well done.


this {{{6(7+5y)/4-2y = -18}}} is not correct as you have +5y..it should be -5y. I guess this was just a simple typo error?.


anyway, correct version is: {{{6(7-5y)/4-2y = -18}}}


First multiply every term by 4:
{{{4*6(7-5y)/4 - 8y = -72}}} so that the fraction in the first term cancels itself:


{{{6(7-5y) - 8y = -72}}}
{{{42 - 30y - 8y = -72}}}
{{{42 - 38y = -72}}}
{{{-38y = -114}}}
y = 3


Now sub this back into eiter equation - pick the one that looks the easiest! I pick the first equation:


4x+5y = 7 becomes {{{4x + 5*3 = 7}}}...


{{{4x + 15 = 7}}}
{{{4x = -8}}}
{{{x = -2}}}


DEFINITELY put these answers in the second equation, to make sure that they equal to -18...


{{{6x-2y}}} becomes {{{6(-2) - 2(3)}}}


{{{-12 - 6}}}
{{{-18}}}


so the answer is DEFINITELY correct.


jon