Answer: Choice C) rate of change is $3 per minute
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The equation is basically in the form y = mx+b where m = 3 is the slope, which is the rate of change for any linear equation
Notice how if x = 0, then c(x) = 2 meaning you pay $2 to get into the cab
If x = 1, then you have gone 1 minute in the cab making the total cost be 3*1+2 = 5 dollars. We've added on 3 dollars after that minute is up. So each minute costs $3. This is the unit rate, where by "unit" I mean 1 minute.
You can also think of it as
slope = rise/run = (change in cost)/(change in time) = (3)/(1)
so each increase of 1 minute leads to a change of cost of $3