Answer:
Step-by-step explanation:
Since the lengths of the shelves are given in cm and the answer is to be expressed in cm, then let's convert the length of the whole board from 2.5 m to cm. Since there are 100 cm in a m, then multiply 2.5 by 100 to get 250 cm. Now let's start with the expressions for the shelves. The lengths of all the shelves are based on the length of the first shelf. You can usually tell which object is the main one because it is mentioned the most number of times. The first shelf is mentioned 3 times so that is the main shelf that the measurements of all the other shelves are based upon. Let's call the first shelf x. The second shelf is 18 cm longer than twice the length of the first so the second shelf is 2x + 18.
The third shelf is 12 cm shorter than the first so the third shelf is x - 12.
The last shelf is 4 cm longer than the first shelf so the last shelf is x + 4. Since he needs to use all 250 cm of the board, we add all the shelves together and set them equal to 250 cm:
x + 2x + 18 + x - 12 + x + 4 = 250 and
5x + 10 = 250 and
5x = 240 so
x = 48. The first shelf is 48 cm long. But we need the length of the second shelf. The expression for the second shelf is 2x + 18, so 2(48) + 18 = 114 cm.
