It is exponent laws. my teacher said x is 3 but i don't get why

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 solution to the equation? k/6.4=8.7 2.3 5.568 15.1 55.68

Solve for n? [tex]z = \frac{3}{4} mn[/tex]