You have 8 certain tricks and a possible 9th trick in either spades or diamonds.
Ideally you would have liked to start by checking whether the diamonds are 3-3 before taking the spade finesse if necessary.
The opposition haven’t allowed you to do this, so you must decide whether to finesse ♠ Q, or play ♠ A and hope diamonds are 3-3.
TAKE THE SPADE FINESSE WHICH IS A 50% CHANCE RATHER THAN HOPING DIAMONDS DIVIDE (A 36% CHANCE).
EVEN IF YOU CAN’T REMEMBER EXACT PERCENTAGES, TRY TO REMEMBER WHICH IS THE BETTER CHANCE OF TWO VERY COMMON SCENARIOS.