You cannot calculate directly,

5x - 4y = 1x + 3y

5x - 1x = 3y + 4y

4x = 7y ...............(1)

suppose if we substitute the value of x as 5 in equation (1), we get,

20 = 7y

y = **20/7**

OR we can substitute, y as 8 in equation (1), we get,

4x = 56

x = 56/4 = **14**