A metal cube dissolves in acids such that an edge of the cube decreases by .60mm per minute. How fast is the volume of the cube changing when the edge is 8.70mm? So we know volume of a cube is side time, side, time side or volume equal X ^3. So the change of volume in terms of time is going to equal 3 X squared. The change of X in terms of time. So three times the radius or the side is given as 8 and 70 hundredth, so 8.70 ^2 the DX DT because it's decreasing, it's going down or it's -.60mm per minute. When we multiply that out, we get negative 136242 and then the directions say to round to the nearest integer, so negative 136. That negative is important because the cube is decreasing. Says how fast is the volume of the cube changing. If we had put in a positive, it would have meant that the cube was getting bigger. But the cube is getting smaller, so the volume has to be decreasing or negative.