Let:
x = Willis Age
y = Heard Age
The difference of their ages is 12 and the sum of their ages is 50, so, let:
[tex]\begin{gathered} x-y=12_{\text{ }}(1) \\ x+y=50_{\text{ }}(2) \end{gathered}[/tex]Using elimination method:
[tex]\begin{gathered} (1)+(2) \\ x+x-y+y=12+50 \\ 2x=62 \\ \text{Divide both sides by 2:} \\ \frac{2x}{2}=\frac{62}{2} \\ x=31 \end{gathered}[/tex]Replace the value of x into (1):
[tex]\begin{gathered} 31-y=12 \\ y=31-12 \\ y=19 \end{gathered}[/tex]Willis is 31 and Heard is 19
