For this case we propose a system of equations:
D: Variable that represents the age of Daniel
B: Variable that represents Ben's age
According to the data we have:
\(B = 3D\\B = D + 4\)
SUBSTITUTING the first equation in the second:
\(3D = D + 4\\3D-D = 4\\2D = 4\\D = \frac {4} {2}\\D = 2\)
So, Daniel is 2 years old.
ANswer:
Daniel is 2 years old.
