Step-by-step explanation:
The formula for law of cosines is:

This is written at the top of your paper.
The angle is substituted where the capital A is. The side opposite to the angle is the angle name's lowercase. The two other sides are b and c.
Substitute all the information you know, then isolate the variable that you do not know.
When your formula is rearranged to look like this:

Solve the left side and punch into your calculator:
cos⁻¹(left side) to find the angle A.