So dad is represented by x son is represented by y
so x is (x=) 7 times his son (7y)
our first sentence is x=7y
10 years later (x+10, y+10) he will be 3 times as old as his son (x+10=3(y+10)) or 10+x=3(y+10)
so our sentences are x=7y and x+10=3(y+10) first we subsitute x=7y for x in the second equation (7y)+10=3(y+10) 7y+10=3(y+10) we distribute 7y+10=3y+30 subtract 3y from both sides 4y+10=30 subtract 10 from both sides 4y=20 divide both sides by 4 y=5
the son is currently 5 years old x=7y subsitute y=5 for y in equation x=7(5) x=35 the dad is currently 35 years old in 10 years dad is 45 and son is 15
