Mary is 21 years old. her age is 9 years more than 3 times henry’s age. which equation can be used to determine x, henry’s age in years?

21-9=12 
12/3=4  
Henry is 4

The second one and the forth one.

The second one because it is true that half of the diameter is the radius.

The forth one because is you do 2 x pi x 31.4 = 197.29 divide that by pi and you get 62.8 pi.

The only reason it is not the third one is because it does not have the step to divide 197.29 by pi.

Hope this Helps!!