Which of the following contains a variable? A. He scored a 95 on the test.
B. The bug crawled 15 inches per second.
C. The area is 56 square centimeters.
D. Ana is 3 years older than Mark.

D. Ana is 3 years older than Mark.

Step-by-step explanation:

We do not know how old Mark is.  That is the variable

d

step-by-step explanation:

d

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