Two trams meet every four minutes, so it takes eight minutes to drive a tram from this distance.

The tram takes 70 minutes, so the distance at this time is 8/70 (the total distance is regarded as 1).

Let Xiao Zhang's speed be 1/x, so (1/70+ 1/x)*5=8/70, so 1/x=3/350.

Similarly, if Xiao Wang's speed is 1/y, then 1/y= 1/2 10.

So when they meet, their usage is actually1(1/x+1/y) =1/(3/350+1/210).

= 1*( 14/ 1050)

=75