Collect like terms together: 3x^2-15x. The 6's cancel out. This factorises (if that's any help) to 3x(x-5). There's no equation (no equals sign) so nothing more can be done, except to graph the function. The zeroes are 0 and 5, which means that the parabolic U-shaped curve cuts the x axis at x=0 and 5 where it dips below the x axis.