Can someone please help me im not sure what the answer is

Which is an equation for the nth terms of the sequence 12,15,18,21

Need ! discuss how to convert the standard form of the equation of a circle to the general form. 50 points

Ascientist has 50 grams of a radioactive element. the amount of radioactive element remaining after t days can be determined using the equation (1) after two days the scientist receives a second shipment of 50 grams of the same element. the equation used to represent the amount of shipment 2 remaining after t days is 10) - 50 which of the following is an equivalent form of the expression for the amount remaining in shipment 2? what’s the answer?