The two equations are:
y=4x+9
y=-1.8x
To solve them, find the place where the two lines intersect or which coordinate they have in common.
You can use substitution in this case because it is easier to make both of the y's equal.
4x+9=-1.8x
5.8x+9=0
5.8x=-9
x= -1.55
Hope this helps :)