5x + y = 27
substitute: 5x + 4x = 27
combine: 9x = 27
divide (by 9): x = 3

Shift the graph of the function y = x², 5 units down /look at the picture #1/.
/look at the picture #2/ - your answer
I think you need to make the 6 positive and then add it to 13 which would give you a=19