Question 1051235
{{{D}}} - Tom's dad's age
{{{T}}} - Tom's age
.
.
.

{{{D=4+2T}}}<---Tom's dad is 4 years older than twice Tom's age
{{{D=40}}}<--- Tom's dad is 40
So then substituting,
{{{40=4+2T}}}<--- They both equal D set them equal to each other.
{{{2T=36}}}<--- Subtract 4 from both sides
{{{T=18}}}<--- Divide both sides by 2