Maths question please answer this

Eric has challenged himself to walk 24,000 steps in 4 days. if eric walks the same number of steps each day, which function represents the number of steps eric still needs to walk to reach his goal with respect to the number of days since he started his challenge? a. y = 8,000x − 24,000 b. y = -8,000x + 24,000 c. y = 6,000x − 24,000 d. y = -6,000x + 24,000

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)

Find the missing factor. write your answer inexponential form.9^2=9^4×