Answer:
Start by substituting the x's with their given value...
1) 5x = 5*4 = 20 20(56a-6y)
2) 56a = 56*1/4 = 14 20(14-6y)
3) 6y = 6*2 = 12 20(14-12)
Now you have to solve what you are left with...
20(14-12)
20*14 = 280
20*12 = 240
280-240 = 40
Your answer is 40
Hope this helps, have a great day! :)