What is this answer, because i've tried it multiple ways and it gives me different answers each time.

If x = 12 and y = 3, what is the value of x - y 2? 81 6 3 18

Iwant to know what 3g+5h+4g-2h is my teacher is too selfish to tell us

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?