There are seven people online and each person uses either a blue, black, or red pen to write while working. How many possible combinations can be made? A. 49

B. 28

C. 21

D. 10

A S A P!! I DONT WANT MY DAD YELLING AT ME FOR THIS ;^;

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?