Question 62850
Well, it looks like you got it all right!..
{{{a/5 + 2b/7 = 1}}}
{{{(7a + 10b)/35 = 1}}}
{{{7a + 10b = 35}}}
{{{10b = 35 - 7a}}}
{{{80b = 280 - 56a}}} Substituting this into the first "equation".
{{{c/2 - 80b = 120}}}
{{{c/2 - (280 - 56a) = 120}}} Simplifying, you get:
{{{c/2 + 56a = 400}}}
{{{c/2 = 400 - 56a}}} Multiplying by 2:
{{{c = 800 - 112a}}}