15=5k-13 whats the letter

Aboat costs 19200 and decreases in value by 12% per year. how much will it cost in 5 years

Nine more than four times a number is the same as one less than twice the number. find the number?

Afactory buys 10% of its components from suppliers b and the rest from supplier c. it is known that 6% of the components it buys are faulty. of the components brought from suppliers a,9% are faulty and of the components bought from suppliers b, 3% are faulty. find the percentage of components bought from supplier c that are faulty.