Given the expression
x + 4y = 9 ............. 1
5x + 10y = 5 .................. 2
We are to get the value of y. To do this, we will have to solve both equations simultaneously by eliminating x;
Multiply equation 1 by 5 and 2 by 1 to give;
5x + 20y = 45 ............. 3
5x + 10y = 5 .......... 4
subtract 3 from 4;
5x-5x + (20y-10y) = 45-5
0+10y = 40
10y = 40
y = 40/10
y = 4
Hence the y-coordinate for solution of the system of equations is 4.