At the beginning of an experiment, a scientist has 100 grams of radioactive goo. After 225 minutes, her sample has decayed to 12.5 grams.

1. What is the half-life of the goo in minutes?

2. Find a formula for G(t), the amount of goo remaining at time t. G(t) =

3. How many grams of goo will remain after 41 minutes?

I got 1. It is 75 minutes

how do you find a formula???