If 18 grams of Ca combines with 22 grams of S to form a compound with a mass of 40 grams, what will be the percent composition of S in the
compound?

The answer for #3 is c but i don't know why

What element breaks down into yttrium-90?

Nitrogen (n), phosphorus (p), and potassium (k) are the main nutrients in plant fertilizers. according to an industry convention, the numbers on the label refer to the mass percents of n, p2o5, and k2o, in that order. calculate the n: p: k ratio of a 30: 10: 10 fertilizer in terms of moles of each element, and express it as x: y: 1.0.