Iam working percentages increases and decreases with problems like from 24 pencils to 30 pencils (increase question) or from 20 miles to 11 miles ( decrease question) how can i check my answers of percentages to make sure they work? !

What is the value of x when x + 7 = 21?

Which of the following quartic functions has x = –1 and x = –2 as its only two real zeroes?

Answer asap ill give ! ’ a sample of radioactive material decays over time. the number of grams, y , of the material remaining x days after the sample is discovered is given by the equation y = 10(0.5)^x. what does the number 10 represents in the equation? a. the half-life of the radioactive material, in days b. the amount of the sample, in grams, that decays each day c. the time, in days, it will take for the samples to decay completely d. the size of the sample, in grams, at the time the material was discovered