Get a constant rate of change

Question

What is a constant rate of changen a task:

When Stephen works overtime babysitting, he charges  $50/8 hours and  $31.25/5 hours

Answer 1

Let's solve this task following the formula:

ΔC / tΔ = (50 - 31.25) / (8 - 5) = 18.75 / 3 = 6.25

So for every extra hour working, he gets additonal $6.25