Why is the domain of this function?

Given the two similar triangles, how do i find the missing length? if a=4, b=5, and b'=7.5 find a'

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)

Analyze the diagram below and complete the instructions that follow. how to find tan