So i don't really understand how to solve this.. here's the question.

the perez family arrived at tia elena's house with 6 gallons of gas. along the way, they first used 8 gallons and then added 10 gallons; then used 5 gallons. how many gallons of gas did the perez family start with? work backward, then solve.

here are the possible answers:

a) 3 gallons
b)7 gallons
c)9 gallons
d)11 gallons

(b) suppose that consolidated power decides to use a level of significance of α = .05, and suppose a random sample of 100 temperature readings is obtained. if the sample mean of the 100 temperature readings is x⎯⎯ = 60.990, test h0 versus ha and determine whether the power plant should be shut down and the cooling system repaired. perform the hypothesis test by using a critical value and a p-value. assume σ = 5. (round your z to 2 decimal places and p-value to 4 decimal places.)