i need help solving this. Can you guys show me how it's done.

Question

Radium-226 decays by alpha emission to radon-222, a noble gas.What volume of pure Radon- 222 at 23oC and 785mmHg could be obtained from 543.0 mg of radium bromide,RaBr2 in a period of 20.2 years.The half-life of radium-226 is 1602 years.

k = 0.693/t_1/2
plug in the half life of Ra-226 and calculate k. THEN, convert 543.0 mg RaBr2 to mg Ra. I will call that value No. Use No in the following formula to calculate N (t is the time of 20.2 years.)
ln(No/N) = kt

From N, which is mg Ra remaining, calculate how much has decayed, convert the amount decayed into mass of Rn-222 and use PV = nRT to calculate the volume Rn at the conditions specified. Check my thinking.