Concept:Age word problems are solved by forming a linear equation for future ages.Explanation:Mensah is currently 5 years old.Joyce is thrice as old as Mensah, so Joyce is 3×5=15 years old.Let x be the number of years after which Joyce will be twice as old as Mensah.After x years: Mensah will be 5+x years old, and Joyce will be 15+x years old.According to the condition: 15+x=2(5+x)Simplify: 15+x=10+2xSubtract x from both sides: 15=10+xSubtract 10 from both sides: x=5Thus, after 5 years, Joyce will be 20 and Mensah will be 10, so Joyce will be twice as old.Answer:5 years (Option C).