Hi there!
Let b equal the weight of Barry's mountain bike. Let a equal the weight of Andy's mountain bike.
b - 6 + b = 42
Since Barry's mountain bike weighs 6 pounds more than Andy's, we can say that Andy's mountain bike weighs b - 6 pounds. Since both mountain bikes added together is 42 pounds, b - 6 + b would be equal to 42.
Hope this helps!
