Let us assume that the number of pieces that can be cut = x
Length of each shelf board = 1 1/3 feet
= 4/3 feet
Total length of board available for making shelf = 18 foot
Then
4x/3 = 18
4x = 18 * 3
4x = 54
x = 54/4
= 13 2/4
As we can see from the above deduction, 13 shelf's can be made from the 18 foot board. There will be about 2/4th of the board remaining, but that 2/4th part will be wasted as it cannot create a complete board.I hope the answer is to your satisfaction and the explanation is clear to you.
let's check how much is it after 2 years firstly.

Brian invested the money for 6 years, so now let's check how much is that for the remaining 4 years.


When paired with 0.23 0.9 is a rational number
You need to substitute the number 6 into the function. The output would be 72, because when l(6) = 12(6), you would get l(6) = 72.
The answer can be readily calculated using a single variable, x:
Let x = the amount being invested at an annual rate of 10%
Let (8000 - x) = the amount being invested at an annual rate of 12%
The problem is then stated as:
(x * 0.10) + ((8000 - x) * 0.12) = 900
0.10(x) + ((8000 * 0.12) - 0.12(x)) = 900
0.10(x) + 960 - 0.12(x) = 900
0.10(x) - 0.12(x) = 900 - 960
-0.02(x) = -60
-0.02(x) * -100/2 = -60 * -100/2
x = 6000 / 2
x = 3000
Thus, $3,000 is invested at 10% = $300 annually; and $8,000 - $3,000 = $5,000 invested at 12% = $600 annually, which sum to $900 annual investment.