If 18 g of a radioactive substance are present initially and 9 yr later only 9 g remain, how much of the substance will be present after 12 yr? After 12 yr there will be g of a radioactive substance.
(Round the final answer to three decimal places as needed. Round all intermediate values to seven decimal places as needed.)

With these 5 geometry questions! pls 1.)quadrilateral abcd is inscribed in this circle.what is the measure of ∠a ? enter your answer in the box.°2.)quadrilateral abcd is inscribed in a circle.what is the measure of angle a? enter your answer in the box.m∠a= 3.)quadrilateral abcd is inscribed in this circle.what is the measure of angle b? enter your answer in the box.m∠b= °4.)quadrilateral abcd is inscribed in this circle.what is the measure of angle a? enter your answer in the box.°5.) quadrilateral abcd is inscribed in this circle.what is the measure of angle c? enter your answer in the box.°