If 21 more than 3 times a number is -15, what is the number?

The number is -12.

Step-by-step explanation:

3x+21=-15

3x=-15-21

3x=-36

x=-36/3

x=-12

-12

Step-by-step explanation:

let the number be x

"3 times a number"  : 3x

"21 more than 3 times a number" : 21 + 3x

"21 more than 3 times a number is -15" : 21 + 3x = -15

Solving this equation:

21 + 3x = -15 (subtract 21 from both sides)

3x = -15 - 21

3x = -36 (divide both sides by 3)

x = -36/3 = - 12

answer: the value of x is 7cm

step-by-step explanation:

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.