Imagine a Cartesian coordinate system with x-axis for time t in hours h and the y-axis for the distance d travelled in km. Both cars are travelling with constant speed. Thus we have two linear functions of the kind y=mx+c, where m represents the slope and c the y-intercept.

Car A has already gone 40km and is travelling at a constant speed of 36km/h. The function, which describes A is:

fA(t) = 36(km/h)*t(h) + 40(km)

Car B starts in the origin of our coordinate system (c=0) with a speed of 48km/h. Thus:

fB(t) = 48(km/h)*t(h)

A) the value of t at the intersection point of the two linear functions fA(t)=fB(t) determines the time it takes car B to catch up with car A:

48t = 36t + 40

12t = 40

t = 3h20m

B) Insert t into one of the functions. As it is the intersection point, they will have the same output at t so it doesn't matter which one you take.

e.g. 48t = 48km/h * 3.3333...h = 160km