Is this right? if it isn't, what IS right?

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.

An ant travels at a constant rate of 30cm every 2 minutes. at what speed does the ant travel per minute

The actual length of side t is 0.045cm. use the scale drawing to find the actual side length of w