Can someone explain to me how to do this problem

Pat listed all the numbers that have 15 as a multiple write the numbers in pats list

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)

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?