Answer:
[tex]b = \dfrac{a - 10c}{10}[/tex]
Step-by-step explanation:
[tex]\begin{array}{rcl}5 & = & \dfrac{a}{2(b + c)}\\\\5& = & \dfrac{a}{2b + 2c}\\\\10b + 10c & = & a\\10b & = & a - 10 c\\b & = & \mathbf{\dfrac{a - 10c}{10}}\\\end{array}[/tex]
