Find the measures of the numbered angles in each rhombus. I need help

The sum of the reciprocal of a positive number and the reciprocal of 2 more than the number is 3/4 equation: the number is

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?

Bob is putting books on a shelf and takes a break after filling 18 1/2 inches on the book shelf. the book shelf is now 2/3 full. how long is the entire bookshelf?