Simplify the following text for a Grade 6 native English-speaking person.
Original: His total earnings on the track were $ 1,491 ( approximately $ as of ) , and his highest speed index , or comparative rating of his speed , was AAA , the highest achievable at the time .
Simplified: His total earnings on the track were $ 1,491 ( $ as of ) . His highest speed index , or comparative rating of his speed , was AAA .