First thing you'll do is add -20y to both sides...
<span><span><span><span>2x</span>+<span>7y</span></span>+<span>−<span>20y</span></span></span>=<span><span><span>−x</span>+<span>20y</span></span>+<span>−<span>20y
</span></span></span></span><span><span><span>2x</span>−<span>13y</span></span>=<span>−x
Next, add </span></span><span>-2x to both sides...
</span><span><span><span><span>2x</span>−<span>13y</span></span>+<span>
−<span>
2x
</span></span></span>=<span><span>−x</span>+<span>
−<span>
2x</span></span></span></span><span><span>−<span>13y
</span></span>=<span>−<span>3x
</span></span></span>Lastly, d<span>ivide both sides by -13...
</span><span><span>−1<span>3y/</span></span><span>−13</span></span>=<span><span>−<span>3x/</span></span><span>−<span>13
Now, your answer is...
</span></span></span>
Good luck with your studies, hope this helps~