A radioactive substance decays at a continuous rate of 12% per year, and 90 mg of the substance is present in the year 2000. (a) Write a formula for the amount present, A (in mg), t years after 2000. MathPAD Response msnViewer_resp_str_c04q_go_2_006_1_svg ViewEdit (b) How much will be present in the year 2010