Level 73 is not that difficult but may require some luck. You can get rid of the granite in the center only with bombs. The bigger the bomb is, the better. Another solution is to match two Lightning power-ups. In this case, it would be more useful to clear only one part of the field (left or right) and try to make as many combo explosions as possible. Don’t waste your moves on single explosions. The drawback of this method is that the power-ups may end up in different parts of the field. At the same time, it’s important to leave a few extra moves to collect any remaining gold nuggets.