Fantastic! Using $$v_{\text{XE}} = 40$$ and $$v_{\text{EY}} = - v_{\text{YE}} = -30$$ in $$v_{\text{XY}} = v_{\text{XE}} + v_{\text{EY}}$$, we get $$v_{\text{XY}} = 40 + (-30) = 10$$
What is the velocity of Car X wrt Car Y in this scenario in $$\mathrm{km/h}$$? Remember Car X is moving at $$40 \, \mathrm{km/h}$$ wrt the Earth and Car Y is moving at $$30 \, \mathrm{km/h}$$ wrt the Earth.
• $$(-40) + (-30)$$
• $$40 + 30$$
• $$(-40) + 30$$
• $$40 + (-30)$$