Can u please help with these questions, they're do in 10 minutes and I have trouble with angles

What are the measures of ∠a, ∠b, ∠c and ∠d? explain how to find each of the angle measure.

If a is a nonzero real number then the reciprocal of a is

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?