Notice that the line intercepts the bottom axis at 9 and also the side axis at 9.
This condition is means that the value you select for one axis relates to the same value on the other axis.
Thus 3 hours watching TV relates to 6 hours sleeping.
One of the standardised forms for the equation of a strait line is:
By observation the y-intercept is 9
So we now have:
We need the value of