We want to find where to put the parentheses on each expression to make the expression true.
First, we identify the symbols +, x, / and - to identify the pairs of numbers. For example, in the expression

we have two symbols (+, *).
Now, this would give us two pairs of expression where we can put the parentheses. That is, one possibility per symbol. So we have

and

Now, let us try the first choice. Remember that first we have to evaluate what is inside the parentheses. This would give us

which coincides to the value we wanted.
In the second case, we have the following symbols / and -
This would give us two pairs for grouping, namely

and

as before, we will first evaluet the first option

If we try the second option, we woud get

which would give us the correct value.