Respuesta :

Answer:

r= 10

Step-by-step explanation:

30 - 20 = 10

Addition Property: For all real numbers x,y, and z , if x=y , then x+z=y+z .

eflexive Property: For all real numbers x , x=x . A number equals itself.

Subtraction Property: For all real numbers x,y, and z , if x=y , then x−z=y−z .

so its subtraction property