Gallium-68 has a half-life of 68 minutes. In how many minutes will a 10 kg sample of gallium-68 decay and reduce to 1.25 kg of gallium-68? can someone plss help me??​

4.25g sample of solid ammonium nitrate dissolves in 60.0g of water in a coffee-cup calorimeter, the temperature drops from 22.0 c to 16.9 c. assume that the specific heat of the solution is the same as that of pure water. calculate delta(h) (in kj/mol nh4no3) for the solution proces.