Another investment question

Susan places $4900 in three investments at rates of 9%, 10.8% and 16.2% per annum, respectively. The total income after one year is $ 640.80 . If the amount placed in the third investment is $900 more than the amount placed in the second, find the amount of each investment.

and also...

The admission fee at an amusement park is $ 1.50 for children and $ 4.00 for adults. On a certain day, 291 people entered the park, and the admission fees collected totaled $824 . How many children and how many adults were admitted?