The equation: Dominic bought a pair of shoes for $90, two t-shirts for $20 each, and four pairs of socks. If he paid 8% sales tax on the entire purchase, and if the total amount of the tax he paid was $12, what was the cost of each pair of socks?

Where I am at thus far:

8/100 (90+2×20+4x) =12

8/100 (130+4x)=12

The answer is supposed to be 5, but I don't know how to get to that.