Ihave been having trouble with this one for a while

The answer is A.

A is correct because...

(7z+23)-(15z+9)       There's an invisible positive 1 in front of (7z+23). Distribute.

7z+23-(15z+9)         Distribute the negative sign among 15z and 9.

7z+23-15z-9            Now, combine the like terms, 7z, and -15z. 7z - 15z

-8z+23-9                 Combine the like terms, 23 and -9. 23 - 9

-8z +14

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.

practice. practice. practice.