18x+4y= -16
9x+7y=17


a
Multiply 1st equation by __ to set up eliminating x by addition.

b
Multiply 2nd equation by __ to set up eliminating x by addition.

c
Multiply 1st equation by __ to set up eliminating y by addition.

d
Multiply 2nd equation by __ to set up eliminating y by addition.