The Answer to this problem is BN=3.8 Units.
A&C
B&F
Try it by fold the prism with paper
For an item that cost $ 42, Mick paid $2.94 in sales tax. So percentage of sales tax is

And we have to find the sales tax that he paid for an item that cost $58, and for that , we have to find 7% of 58 , that is

So he pays a sales tax of $4.06 .