(this is a section under differential equations)

Problem 5: It is known that 206 gram of Plumb is produced owing to the radioactive decay of 238 gram of Uran. Determine the age of a rock, where the relation of Uran mass to Plumb mass is equal to 50:7. The half decay time of Uran is equal to 4.5 X 109 years. Assume that at t = 0 the mass of Plumb is equal to zero