Question 4.2.5: Write “the sum of an unknown and 6, when divided by 15, is e......

 \begin{matrix}^{\mathbf{The\ sum\ of\ an}}_{\mathbf{unknown\ and\ 6}} & ^{\mathbf{when\ divided}}_{\mathbf{\ \ \ \ \ \ \ \ \ by\ 15}}& ^{\mathbf{\ \ \ \ \ \ is}}_{\mathbf{equal\ to}}& ^{}_{\mathbf{7.}} \\ \mathbf{\downarrow} & \ \ \ \mathbf{\downarrow} & \mathbf{\downarrow} & \mathbf{\downarrow} \\ (r + 6) & \div 15&= &7 \end{matrix}

Simplify and solve the equation.

             (r + 6) ÷ 15 = 7

(r + 6) ÷ 15 • 15 = 7 • 15      Multiply both sides by 15.

                       r + 6 = 105

                r + 6 – 6 = 105 – 6     Subtract 6 from both sides.

                            r = 99