write a decimal addition problem that can be solved mentally using the commutative and associative properties.

5=812a+9+3

step 1: simplify both sides of the equation.

5=812a+9+3

5=(812a)+(9+3)(combine like terms)

5=812a+12

5=812a+12

step 2: flip the equation.

812a+12=5

step 3: subtract 12 from both sides.

812a+12−12=5−12

812a=−7

step 4: divide both sides by 812.

812a /812 = -7/812

a= -1/116

so the answer is

a=   -1/116

b is the right answer

you meant circumference well the answer is:

17.27876 miles

area is 23.7583

the radius is 2.75 miles

hope this hmu if needed.