Question 344378
{{{A}}}-Alec
{{{B}}}-Alisa
{{{C}}}-Ivan
.
.
1.{{{A=B+10}}}
2.{{{A=2C}}}
3.{{{A+B+C=50}}}
From eq. 1,
{{{B=A-10}}}
From eq. 2,
{{{C=A/2}}}
Substitute both results into eq. 3,
{{{A+(A-10)+A/2=50}}}
Multiply both sides by {{{2}}},
{{{2A+2(A-10)+A=100}}}
{{{2A+2A-20+A=100}}}
{{{5A-20=100}}}
{{{5A=120}}}
{{{highlight(A=24)}}}
Then 
{{{B=24-10}}}
{{{highlight(B=14)}}}
And finally,
{{{C=24/2}}}
{{{highlight(C=12)}}}
.
.
.
Alec is 24, Alisa is 14, and Ivan is 12.