Can i get some help pls i don't know how to write this equation

 x = (log(y) /(400 log1.0065) or x = log(initial cost)/1.126

Step-by-step explanation:  Take the log of both sides of your equation:

log(y) = log(400)(1.0065)^x

log (y) = log 400 + log(1.0065)^x

Subtract log(400) from both sides:

log(y) - log 400 = xlog(1.0065)

Divide both sides by log(1.0065)

[log(y) - log(400)]/log(1.0065) = x

Now, if you want to know how many years it will take for the guitar to be worth $200, replace y with 200 and solve.

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step-by-step explanation:

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