Could someone please solve this and explain how to do it?

An arc subtends a central angle measuring 7pi/4 radians what fraction of the circumference is this arc?

What happens to the area as the sliders are adjusted? what do you think the formula for the area of a triangle is divided by 2?

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.