You have 240 grams of a radioactive kind of tellurium. How much will be left after 210 minutes if it

You have 240 grams of a radioactive kind of tellurium. How much will be left after 210 minutes if its half-life is 70 minutes?

if the half life is 70 minutes, then we have 210/70 = 3 half life cycles.

So the first half-life is 240 * 1/2 = 120
The second half life is 120 * 1/2 = 60
The third half life is 60 * 1/2 = 30 grams