12 less than a number , x
A 12 - x
B x - 12

Me because some of question i don’t understand

Jenisey has $24 to spend on seven pencils. after buying them she had $10. how much did each pencil cost.?

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?