It takes 2 1/4 kilometers of thread to make 3 1/2 boxes of shirts. how many kilometers of thread would it take to make 8 boxes?

Kilometers of thread.

The key to solve this problem is using the rule of three.

We have to change mixed number to improper fraction in order to solve the problem.

A mixed number is a number formed by an integer and a proper fraction (one whose quotient is less than 1).

An improper fraction  is one whose denominator is less than its numerator.

To change a mixed number to an improper fraction:

1. Multiply the whole number by the denominator and add to the numerator.

2. The denominator of the mixed number is unchanged.

It takes kilometers of thread to make boxes of shirts. How many kilometers of thread would it take to make 8 boxes?

We need to change and to an improper franctions:

To calculate how many kilometers of thread would it take to make 8 boxes, we use the rule of three:

9/4 Km of thread -------------> 7/2 boxes of shirts

                    x     <-------------  8 boxes of shirts

Convert the improper fraction 38/7 to a mixed number:

1. Divide the numerator by the denominator.

38÷7 = 5 and a remainder of 3

2.  5 become the whole number, the remainder is the numerator, and the denominator is unchanged.

38/7 = 5 3/7

It would take 5 3/7 kilometers of thread make 8 boxes of shirts.

Im guessing 21 and 72 are the side lengths for the triangle?

Alright, so since it's a right triangle you can use the Pythagorean theorem or a^2+b^2=c^2

Since i cant see the picture, im going to use some general math so i can figure out if those two sides are the legs or if one of them is the hypotenuse
Alright 
so im guessing the side we're trying to find is the hypotenuse

21^2+72^2=c^2
441+5184=c^2
5625=c^2
√5625=c
75=c

The answer is 75, hope i helped!