Changing the equations into a matrix, we have:
1 1 1
4 -1 0
1 -19 -15
Second row minus four times first row and third row minus first row:
1 1 1
0 -5 -4
0 -20 -16
third row minus four times second row:
1 1 1
0 -5 -4
0 0 0
Multiplying second row by -1/5:
1 1 1
0 1 4/5
0 0 0
first row minus second row:
1 0 1/5
0 1 4/5
0 0 0
Hence, we have:
x = 1/5 and y = 4/5