In $2002,$ one dollar bought $120.$ In $2006,$ it bought about $100.$

$($a$)$ What was the dollar value of the yen in $2002$ and $2006?(10$ pts$)$

$($b$)$ By what percent had the yen risen between $2002$ and $2006?(10$ pts$)$

$($c$)$ By what percent had the dollar fallen between $2002$ and $2006?(10$ pts$)$