Your equation is correct.

The acceleration due to gravity on earth is g = 32.174 ft/s².
Therefore on Mars,
g = (2/3)*32.174 = 21.45 ft/s²
When an object falls from rest over a distance h, the final velocity, v, obeys the equation
v² = 2gh
or
v = √(2gh)
Therefore, given h = 15 ft, the impact velocity on Mars is
v = √(2*21.45*15) = 25.367 ft/s
The closest given answer is 25.3 ft/s
Answer: B) 25.3 ft/s
When you add a positive and a negative like you did here it basically is the same as subtracting 5 from 3
Answer: 2.460
Step-by-step explanation:
The formula of Margin of Error for (n<30):-

Given : Sample size : n= 18
Level of confidence = 0.90
Significance level : 
Using the t-distribution table ,
Critical value : 
Standard deviation: 
Then, we have

Hence, the margin of error (ME) of the confidence interval with a 90% confidence level = 2.460