Answer :
Answer: the store charged $40 for the bike helmet before tax.
Step-by-step explanation:
Let x represent the amount that the store charge for the bike helmet before tax.
If the sales tax rate was 8%, it means that the amount of tax that was charge is
8/100 × x = 0.08 × x = 0.08x
Monica paid sales tax of $3.20 when she bought a new bike helmet. This means that
0.08x = 3.2
Dividing the left hand side and the right hand side of the equation by 0.08, it becomes
0.08x/0.08 = 3.2/0.08
x = 40