Question 878846
Your given system is ready for using the Elimination Method, but you want "addition-subtraction" method.  This name of method is not well known everywhere, so I will show you how to begin the solution process of the Elimination Method.


Both of your equations are in standard form and both have a term, 5y in their left members.  


{{{2x+5y-(3x+5y)=15-10}}}
{{{2x+5y-3x-5y=5}}}
{{{2x-3x+5y-5y=5}}}
{{{-x+0=5}}}
{{{-x=5}}}
{{{highlight(x=-5)}}}
-
I prefer to continue using substitution.
Start with either original equation, arbitrarily choosing----3x+5y=10
{{{5y=10-3x}}}
{{{y=10/5-3x/5}}}
{{{y=2-3x/5}}}
{{{y=2-3*(-5)/5}}}
{{{highlight(y=5)}}}