Monica paid sales tax of 1.50 when she bought a new bike helmet . if the sales tax rate was 5% how much did the store charge for the hemelt before tax

Let h be the price of the helmet (not hemelt).  Then 0.05h= $1.50.
To determine the price of the helmet, divide both sides of this equation by 0.05:

h = $30

The helmet is $30 before sales tax is applied, and $31.50 with tax.