Please help. I can't figure it out how to write proofs

Twice the sum of a number and 4 is equal to three times the difference of the number and 7. find the number.

A. 127 cm^2 b. 144.5 cm^2 c. 172 cm^2 d. 50 cm^2

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