Please helpl 20 points, its hard

Tim's phone service charges $26.39 plus an additional $0.21 for each text message sent per month. if tim's phone bill was $31.64, which equation could be used to find how many text messages, x, tim sent last month?

Solve -.016x= -16. need solving this

In the diagram, ab is tangent to c, ab = 4 inches, and ad = 2 inches. find the radius of the circle.