Question

Ben is one more than two times as old as cheryl. In six years the sum of their ages will be 100. How old is Cheryl now?

Answer 1

$b=1+2c$
$(b+6)+(c+6)=b+c+12=100$

Substituting the first equation into the second, you get

$1+2c+c+12=3c+13=100\implies 3c=87\implies c=29$

so Cheryl is currently 29 (while Ben is $1+2\times29=59$).