Helen has 21 marbles. 2/7 of them are blue,1/3 are red and the rest are green. how many green marbles does Helen have?

Multiply. −2x(6 x 4 −7 x 2 +x−5) express the answer in standard form. enter your answer in the box.

Select all the correct answers. what is 221,000,000,000,000,000,000 expressed in scientific notation?

Grace is standing 18 feet from a lighthouse and kelly is standing 10 feet from grace. the angle that grace looks up to see the top of the lighthouse is 45°. the angle that kelly looks up to see the top of the lighthouse is y°. find the height, h, of the lighthouse. find the angle, rounded to the nearest tenth of a degree, in which kelly looks up to the top of the lighthouse. to the nearest tenth of a degree, find the value of x° . in two or more sentences, explain your calculations