Question 825000
Let S = Sean's age, and D = Doug's age.

Write it out as these equations:

{{{S = 2D+5}}}
{{{S+D = 29}}}

Use the system of elimination to subtract the second equation from the first one and isolate Doug's age.

{{{-D = 2D-24}}}
{{{D = -2D+24}}}
{{{3D = 24}}}
{{{D = 8}}}

Plug Doug's age into one of the equations.

{{{S+8 = 29}}}
{{{S = 21}}}

Sean's age is 21, and Doug's age is 8.