Let f(t) be the weight (in grams) of a solid sitting in a beaker of water ...

 Let f(t) be the weight (in grams) of a solid sitting in a beaker of water. Suppose that the solid dissolves in such a way that the rate of change (in grams/minute) of the weight of the solid at any time t can be determined from the weight using the formula: f′(t)=−4f(t)(5+f(t))
If there is 1 grams of solid at time t=2 estimate the amount of solid 1 second later.