When Sam is 13 his mother will be 39 which is 3 times as old as he is. So Sam's mother will be 3 times as old as Sam will be in 11 years. (Your answer is 11 years.)
Known :
1 kg = $20
Asked :
½ kg = $...?
Answer :
1 kg = $20
½ kg = ½ × $20
= <u>$</u><u>1</u><u>0</u>
<em>Hope it helps and is useful</em><em> </em><em>:</em><em>)</em>
5/8- I think that is the right answer