Question on superheterodyne FM receiver to find the range of local oscillator and the image station ...?
Your answers are correct.  Another way to think about the image is, that you'd set the oscillator to 18 MHz (so that 18-10 MHz gives 8 MHz for the I.F.).  With that setting, you can pick up a signal that's 8 MHz away in the other direction, that being 18+8 MHz, which is the answer you got.