3/10+(−7/20) enter your answer as a fraction, in simplified form i need quick

Which equations represents circles that have a diameter of 12 units and a center that lies on the y-axis? check all that apply

Answer! if you don’t mind, can you explain

Which of the following is an example of a rational number? a. π b. √ 9 c. √ 8 d. 3.8362319