Mick would pay $4.06 in sales tax for an item that costs $58.00.
This can be found by working backwards in the problem. By dividing that sales tax paid (2.94) by the dollars before tax (42), you get a percentage that should equal the percentage of the total paid for tax.
2.94 ÷ 42 = 0.07
This means that the sales tax is 7% of the total prior to tax. So we'd then multiply our dollars (58) with the sales tax in decimal form (0.07)