Nathan buys a bottle of water for $1.25, gum for $0.50, and a book for $3.95. The sales tax is 10%. What is the sales tax for the things he buys?

take the logarithm of both sides (the base of the log doesn't matter):

apply the exponent property - this says that :

distribute the log terms on both sides:

group like terms together:

divide through both sides by the coefficient on :

you can do some additional rewriting here using the properties of the logarithm to simplify things if you like: