Aused truck for $4,500 he made an agreement with the dealer to put $1,500 and make payments of 350 for the next 10 months that extra costs paid by taking this bill bill is equivalent to what actual yearly rate of interest

Ist amount paid = $1500
Making $350 for 10 months = 10*350 = $3500
Total amount paid  = 1500 + 3500 = 5000
So an amount of $5000 was paid to cover the cost of $4500 within the ten month period.
I = PRT
Interest, I = 5000 - 4500 = 500Time, t = 10 months = 10/12 = (5/6) year.Principal P = 4500
R = I /(PT)  R = 500 / (4500*5/6)
R = (500*6) / (4500*5)
R = 0.1333..
R ≈ 13.33 %  per annum.

If you need an equation, it would be y=2x+8, y would be how long it grew, x being weeks.if you need how long he was asleep, it would be 4 weeks if he started with no beard, the equation would be x=8÷2if he did have a beard before hand, the equation would be 2w+x=8