SOLVE: (x+k) (x²-l²)= 0
Is this correct: $\displaystyle (x+k)(x^2-l^2) = 0$ ? If so, have you seen the 'difference of two squares' rule? You might want to apply it to the second factor then.
Also, 0*a = 0 for any number a, so, if you can make any of your factors 0, then the whole left hand side will be 0, which is what you want. Can you see what x you would have to choose in each factor to make it equal to 0?