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: $$f'(t) = -4\, f(t)\, ( 4 + f(t) )$$

If there is 2 grams of solid at time $t=2$ estimate the amount of solid 1 second later.