Given data:
The current price of the guitar is P=$315.
The sale tax on the guitar is T=8%.
The expression sales tax amount is,
S=TxP
Substitute the given values in the above expression.
S=(8%)($315)
=(0.08)($315)
=$25.2
The expression for the total cost of the guitar is,
T=P+S
substiute the above-calculated vale and given value in the expression.
T=$315+$25.2
=$340.2
Thus, the final cost of the guitar is $340.2.