A=1/2 bh; solve for b
b = 2A/h
To isolate b, you should first “get rid” of the 1/2. The best way to do this to multiply both sides of the equation by 2. The left side becomes 2A, while the right becomes bh (1/2 multiplied by its reciprocal, 2, becomes 1). Next, you have to move the h to the left side, and you could do so by dividing both sides by h. The left side becomes 2A/h, and the right is just b by itself, getting you b = 2A/h.