The legs of a right triangle have lengths of 28 meters and 21 meters. the hypotenuse has a length of 5x meters. what is the value of x?

We have a right triangle with
a = one leg = 28
b = other leg = 21
c = hypotenuse = 5x

use the pythagorean theorem (a^2+b^2 = c^2) and solve for x

a^2+b^2 = c^2
28^2+21^2 = (5x)^2
784+441 = 25x^2
1225 = 25x^2
25x^2 = 1225
(25x^2)/25 = 1225/25
x^2 = 49
sqrt(x^2) = sqrt(49)
|x| = 7
x = 7 or x = -7

Since the hypotenuse has length 5x meters, this means
5x = 5*7 = 35
or
5x = 5(-7) = -35

Toss out the negative length as it makes no sense. 

The only value of x is x = 7

Therefore the final answer is x = 7

1. 0.3 •4 is the same as 4 groups of 0.32. 7•0.8 is the same as 7 groups of 0.83. it increases by 0.5 every time, so 0.5x4 it increases by 0.9 every time, so 0.9x5. 0.9•12=10.86. 0.47•5=2.35i can finish the next ones in a separate post

Understanding what? lol