ive been doing this type of stuff in my class.
so to find this you need to first:
multiply 40 * 2
and multiply 60 * 3
= 80
= 180
add 180 + 80 = 260
add the time together so 2 + 3 is 5
divide 260 / 5 = with an answer of 52km/h
i hope this helps, if incorrect or mis proper answer let me know :)
-wolfs