Question 342360
Let the Father's age be {{{F}}}, the son's {{{S}}}. 
In 6 years their ages are {{{F+6}}} and {{{S+6}}}.
1.{{{F=4S}}}
.
.
.
{{{(F+6)+(S+6)=57}}}
{{{F+S+12=57}}}
2.{{{F+S=45}}}
Substitute eq. 1 into eq. 2,
{{{4S+S=45}}}
{{{5S=45}}}
{{{highlight(S=9)}}}years old
Then from eq. 1,
{{{F=4(9)}}}
{{{highlight(F=36)}}} years old