Question 1089955
Find: how old is martin in 10 years
Let:
martin = x
kris = y 
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Given: 
is means equal 
eq 1: {{{x=y+8}}}
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in 10 yrs means +10
eq 2: {{{y+10=(x+10)/4 +7}}}
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Solution
Substitute eq 1 to eq 2
{{{y+10=((y+8)+10)/4 +7}}}
{{{4(y+10)=4((y+8)+10/4 +7)}}}
{{{4y+40=((y+8)+10) +28}}}
{{{4y+40=(y+18) +28}}}
{{{4y+40=y+46}}}
{{{3y+40=46}}}
{{{3y=6}}}
{{{y=2}}}age of kris
{{{x=2+8}}}
{{{x=10}}} age of martin
{{{x=10+10}}}
{{{x=20}}} age of martin in 10 years!