-3 I think because 9x3= 27 so 9x-3= -27
When we are multiplying our 10's, we are basically adding another 10 each time. Since the number grid is in rows of 10, adding another 10 is the same as moving down one row, which makes a straight column.
Solve for x
6x+5y=-15
subtract 6x from both sides
5y=-6x-15
divide both sides by 5
y=-6/5x-3