For part a, only one of the four boxes is correct. Which is it?

Recall your order of operations, which is what you have probably just learnt recently.

Brackets first.
Division and/or multiplication next, whichever comes first.
Addition and/or subtraction next, whichever comes first.

I use / for the division symbol.

30 + 48 / 3 x 2

I see a +, then a /, then a x. No brackets. Which one should I calculate first?

I see the plus. I might think, “30 + 48 = 78”.

But then, immediately after the plus is a divide, and after that is a multiplication (without brackets).

So, we do division first since it comes before the multiplication and it takes priority over the plus.

30 + 48 / 3 x 2
= 30 + 16 x 2

Should we now do 30 + 16 first or 16 x 2 first?

Now, the multiplication takes priority over the addition, so we complete the multiplication first.

30 + 16 x 2
= 30 + 32

With no other operation in sight, we add the remaining to obtain 62.

Let you do part b on your own first, then see if you are able to follow the order. Memorise the order and try to use the order first.