Your equation looks like this:
[tex]bX\frac{1}{8} =\frac{2}{3} [/tex]
All you have to do is divide 2/3 by 1/8. Without using a calculator, we can do this through the Keep Change Flip method. Keep the first faction 2/3, change the ÷ to a ×, and flip the 1/8 to 8/1. Now we multiply as usual:
b = 2/3 × 8/1
b = 16/3
