Situation: Find Round A 31 gram sample of a substance that's a by-product of fireworks has a k-value of 0.1173. N= Noekt No = initial mass (at time t = 0) N = mass at time + k = a positive constant that depends on the substance itself and on the units used to measure time t = time, in days Find the substance's half-life , in days .
Round your answer to the nearest tenth.​

Expresa commuter train leaves downtown sation and travels at a average speed of 55 miles per hour towards the north side sation, which is 50miles away. thirty minutes later, express commuter train #7 leaves north side and travels at a average speed of 35miles per hour towards downtown sation. at the moment the two trains pass each other, how far(in miles) is train #12 from the downtown sation and how long(in minutes) has the #12 train been traveling