the amount of simple interest on a deposit varies jointly wi

the amount of simple interest on a deposit varies jointly with the principal and the time in days.if $6.66 is earned on a deposit of $3700for 8 days ,how much interest would be earned on a deposit of $4500for 24 days?

Solution

$ 6.66 is earned on deposit of $ 3700 for 8 days

let x be proportionality constant

simple interest on a deposit varies jointly with the principal and the time in days

SI = x * P * t

x = SI / P*t = 6.66 / 3700 *8 = .000225

now SI on $ 4500 for 24 days

SI = .000225 * 4500* 24 = $ 24.3

interest = $ 24.3