If you know the area of a circle, how can you find is radius

What is the value of x in the diagram below?

Galen sold tickets of his church’s carnival for a total of $2,820. children’s tickets cost $3 each and adult tickets cost $5 each. the number of children’s tickets sold was 30 more than 3 times the number of adult tickets slod. how many children’s ticket and how many adult tickets did he sell?

The trigonometric ratios sine and secant are reciprocals of each other