Solve for x. No links please

Bring the fraction a/a-4 to a denominator of 16-a^2

Circle a has a diameter of 7 inches, a circumference of 21.98 inches, and an area of 38.465 square inches. the diameter of circle b is 6 inches, the circumference is 18.84 inches, and the area is 28.26 square inches. part a: using the formula for circumference, solve for the value of pi for each circle. (4 points) part b: use the formula for area and solve for the value of pi for each circle. (4 points)

Which is the standard form for this number? (2 x 10) + (5 x 1) + (8 x 1 10,000 )