$4680
Since 18% is 18/100 you just have to multiply the $842.4 by the reciprocal of that to find your answer
Reciprocal of 18/100 is 100/18
842.4* 100/18 equals 84240/18
84240/18 equals 4680
Answer:
B
Step-by-step explanation:

subtract 6 from both sides

divide by 2/3(or multiply by 3/2)

and thats your answer
This is a compound interest problem so you cannot use the simple interest formula. Effectively the total amount is being compounded each year by 6%. There is a formula for compound interest but in this simple example you can work this out recursively.
year 1 = 6500
year2 = 6500*1.06 = 6890
year3 = 6890*1.06 = 7303
year4 = 7303*1.06 = 7741..
etc......
year12 = 11604*1.06 = 12338
18 ft* (1 piece/ 1 1/3 ft)= 13.5 pieces.
Mr. Gengel can only cut 13 pieces from the big board (because we don't have half a piece)~