If $4200 is invested into a savings account for which interest is compounded semiannually, and if the $4200 turns into $4900 in 4 years, what is the interest rate of the savings?

We just started the introduction into circles and i have no idea how to do this.

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?

Which is the solution to the inequality? 2 3/52 1/15 b< 3 2/15 b> 3 2/15