NEED HELP ASAP PLEASE! WILL GIVE BRAINLIEST

Find the sales tax.

I need a explanation on how you got the answer. So justify your answer please.

Me n o w. i need t h i s. 10 points

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.

See attachment below and find the equivalent of tan(∠qsr)