Aliana has $42.50
if she wants to buy a sweater that cost $29
and some pairs of socks $4.50 each
in this case
x is the number of pairs of socks that Aliana can buy
so the equation is
29+4.50x=42.50
we need to clear x
4.50x=42.50-29
4.50x=13.50
x=13.50/4.50
x=3
she can buy 3 pairs of socks