Sales tax rate of of $4.00 if the total cost is $4.32

Make a proportion. We know $4 is 100% and $4.32 is 100% plus taxes

so $4 = 100% and 4.32 = x

Cross multiply

4x = 4.32*100%

4x=432%

divide by 4

x=108%

since 4.32 is 100% + taxes, you have to get taxes alone by subtracting 108% by 100% leaving us with

8% sales tax