please help WITH THIS

Question

At the beginning of an experiment, a scientist has 396 grams of radioactive goo. After 225 minutes, her sample has decayed to 12.375 grams. 

What is the half-life of the goo in minutes?  $5

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

How many grams of goo will remain after 53 minutes?

Answer 1

G(t) = 396 * (12.375/396)^(t/225) = 396 * (1/32)^(t/225) = 396 * (2^-5)^(t/225) = 396 * 2^(-5t/225) =

396 * 2^(-t/45)

The half-life is 45 minutes.

After 53 minutes, the amount of goo is 396 * 2^(-53/45) = 396 * 2^-2*2^(37/45) = 99 *2^37/45 = 175.0446