okay, so with these equations, you collect 'like terms.' like terms are basically grouping things that are the same together, so for example a+a-b+2b would be 2a+b.
with this equation you want to do the same.
2/3b + 5 = 20 - b
first, make all the numbers integers (whole numbers). we want to make 2/3b a whole number, so we multiply the whole equation by 3 to keep everything in proportion with each other, thus ending up with
2b + 15 = 60 - 3b
now we collect 'like terms.'
add 3b to both sides gives
5b + 15 = 60
subtract 15 from both sides
5b = 45
divide by 5 to leave the value of b
b = 9
