What are the rules for adding and subtracting negative and positive decimals

Express the following as a function of a single angle, cos(60) cos(-20) - sin(60) sin(-20)

Which of the following is a proper fraction? a. 9⁄8 b. 5⁄6 c. 7⁄3 d. 4⁄2

He mass of a single atom of carbon can be found by dividing the atomic mass (12.01 g) by 6.022 x 10^23. which is the mass of a single carbon atom, correctly written in scientific notation with the correct number of significant figures?