Nine days ago, the Area covered by the Piece of Bread was 3 sq inches Total the Mould covers 9 sq inches What is the Rate of Change in the Mould Area

Answer: 2/3 square inch each day

Solution: 

The mould covered 3 square inches 9 days ago.

The current area covered by the mould is =  9 square inches.

The difference in the mould coverage area is = 9-3=6 square inches.

In 9 days, a 6 equitable inch growth happened.

The growth rate in mould’s site is now defined as Change in the area occupied / time taken.

the Rate of Change = 6/9 = 2/3   

The area of mould changes at a pace of 2/3 square inches each day.