Answer
See the picture.
Now, the slope of the lines changes as $x_2$, in first case, or $x_1$, in the second case, change.
Work Step by Step
$ŷ=4+0.4x_1-1.3x_2+0.05x_1x_2$
- For $x_2=10$:
$ŷ=4+0.4x_1-1.3\times10+0.05x_110=-9+0.9x_1$
- For $x_2=20$:
$ŷ=4+0.4x_1-1.3\times20+0.05x_120=-22+1.4x_1$
- For $x_2=30$:
$ŷ=4+0.4x_1-1.3\times30+0.05x_130=-35+1.9x_1$
- For $x_1=40$:
$ŷ=4+0.4\times40-1.3x_2+0.05\times40x_2=20+0.7x_2$
- For $x_1=50$:
$ŷ=4+0.4\times50-1.3x_2+0.05\times50x_2=24+1.2x_2$
- For $x_1=60$:
$ŷ=4+0.4\times60-1.3x_2+0.05\times60x_2=28+1.7x_2$
