The > symbol shows that you have to be older than 13, and there must be a line underneath to signify a can be equal to the number (meaning you can be 13 to do this).
using the two angles in the triangle, 1 and 2, it can be 180- the sum of angles 1 and 2, which is c. using angle 4, it can also be 180 - the equation for angle 4
