A radioactive element decays someone please help

Question

A radioactive element decays into non-radioactive substances. In 980980 days the radioactivity of a sample decreases by 6565 percent. Give your answer to the following questions round to the nearest whole number of days.

(a) What is the half-life of the element?

half-life:    (days)

(b) How long will it take for a sample of 100100 mg to decay to 9595 mg?

time needed:    (days)

Answer 1

decays 65% in 980 days

A =Pe^rt

let P = 100

A = 350

t=980

.35 = e^980r

ln.35 = 980r

r = ln.35/980

half life is when

.5 = e^rt = e^(ln.35/980)t

ln.5 =tln.35/980

t = 980ln.5/ln.35 = about 647 days

time for 100 to decay to 95

.95 = e^(ln.35/980)t

ln.95 = tln.35/980

t = 980ln.95/ln.35 = about 48 days