Some carpet cleaning costs are shown in the table. the relationship is linear. find and interpret the rate of change

Y = m x + b , where m is the slope. The slope is the rise over the run or the change in x ( rooms cleaned ) over the change in y ( cost ).
125 = m * 1 + b
175 = m * 2 + b

b = 125 - m
175 = 2 m + 125 - m
m = 175 - 125
m = 50 ( the rate of change ),  b = 75
The formula is:  y = 50 x + 75
It means that the starting cost will be $75 and that for every room cleaned, the cost will rise for $50. 

Ithink if ur looking for a ratio it would be 12: 3