start by bringing all b's to one side of the equation and all constants to the other
[tex]\frac{2}{3}b+b=20-5[/tex]simplify both sides, remembering that 1 can be written as 3/3
[tex]\frac{2}{3}b+\frac{3}{3}b=20-5[/tex]since the fractions have the same denominator, we mantain the denominator and add the numerator together
[tex]\frac{5}{3}b=15[/tex]multiply both sides by 3
[tex]\begin{gathered} \frac{3\cdot5}{3}b=15\cdot3 \\ 5b=45 \end{gathered}[/tex]divide both sides by 5
[tex]\begin{gathered} \frac{5}{5}b=\frac{45}{5} \\ b=9 \end{gathered}[/tex]