Your answer is 127.5 is 250% of 51
-5x+4y=11
substitute for x which is 5
(-5)(5)+4y=11
simplify :
4y-25=11
add 25 on both sides
4y-25=11
+25 +25
the 25 cancels out
so it would be 4y=36
and you divide both sides by 4
4/4 =36/4
which gives you (5,9)
x= 5 , y =9