Robert needs to cut four shelves from a board that is 2.5 meters long. the second shelf is 18 centimeters longer than twice the length of of the first shelf. the third shelf is 12 centimeters shorter than the first shelf. the remaining shelf is 4 centimeters longer than the first shelf. if robert must use the entire 2.5 meter board for the shelves, what is length of the second shelf, in centimeters ?

There are 100 centimeters in a meter.

therefore 2.5 meters = 2.5 * 100 = 250 centimeters.

x = the length of the first board.
2x + 18 = the length of the second board.
x - 12 = the length of the third board.
x + 4 = the length of the fourth board.

the total length of all the boards is equal to 5x + 10,

since the total length of the board is 250 centimeters, then you get:

5x + 10 = 250

solve for x to get x = 48 centimeters.

the 4 board lengths are:

x = 48
2x + 18 = 114
x - 12 = 36
x + 4 = 52

add them up and you get a total of 250 centimeters.

250 centimeters / 100 = 2.5 meters.

this confirms the solution is good.
 Hope this helps!

Okay so for every triangle has three angles that always add up to 180 degrees. and to tell the difference between whether they are secure, right or obtuse is that acute: has one angle that is less than 90 degrees. right triangle means there is at least one angle that is exactly 90 degrees. and an obtuse angle has an angle that is bigger than 180 degrees. i’ll do #13 as an example: 13. 40 and 50 so if every triangle has 180 degrees 40+50= 90 degrees then180-90= 90 degrees so the third angle is 90 degrees and because this triangle has a 90 degree angle it means it is a right triangle