Answer:
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Recall your d = rt, distance = rate * time.
notice, the distance are the same, say it was "d" miles.
and if car A is travelling at a speed of say "r" mph, then B is going at "r+15" mph.

how far is B going? well, r + 15.
Part 2 is 12.5 cm represents 5km
I worked this out by doing a ratio
5cm=2km
?cm=5km
you have to do 2 times 2.5 to get 5km so you do 5 times 2.5 to get 12.5cm
so the answer is that 12.5cm
Step 1: 6x - 2x - 5 = -6 + 21
Step 2: 6x - 2x - 5 = 15
Step 3: 4x - 5 = 15
The next step would be to add 5 to both sides of the equation.
so Step 3: 4x - 5 = 15 .......add 5 to both sides would make
Step 4: 4x = 20
So after the next step you would have 4x = 20
Hope this helps! :)