How to do question 4 and 5?

How do i do this? i don’t understand

The trigonometric ratios sine and secant are reciprocals of each other

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?