Luis wants to buy a skateboard that usually sells for 79.99 all merchandise is discounted by 12% what is the total cost of the skateboard if luis has to pay a state sales tax of 6.75%

Can someone answer these problems for me

The number of revolutions of two pulleys is inversely proportional to their diameters. if a 24-inch diameter pulley making 400 revolutions per minute is belted to an 8-inch diameter pulley, find the number of revolutions per minute of the smaller pulley.

Ageologist had two rocks on a scale that weighed 4.6 kilograms together.rock a was 0.5 of the total weight.how much did rock a weigh?