Zener voltage regulator circuit
The maximum load current is when then zener no longer has sufficient current to regulate. Since we don't have any information about the Zener diode itself, we can assume it to be perfect so it stops regulating when the zener current drops to zero. That's actually a reasonable assumption for an 8V zener.
The worst-case conditions on the low side are minimum input voltage, maximum resistor value within tolerance (we're not given tolerance so assume it to be perfect) and maximum load current.
You should be able to calculate this, as this is a homework problem we don't give complete answers, but this should be enough of a hint.