What is the percent change if 15 is increased to 21?

Will mark brainliest if you answer ! the taco shop sold 198 lunches friday. this number is 3 more than 3 times the number they sold monday. let n represent the number of lunches sold monday. which equation shows an equality between two different ways of expressing the number of lunches sold on friday? a. n – 3 = 198 b. 3n – 3 = 198 c. 3n + 3 = 198 d. n + 3 = 198

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.

Varies inversely with x. if y=8.5 when x=-1 find x when y=-1