Word problem: solving with 3 variables:

Lila has three investments totaling $100,000. These investments earn interest at 7%, 9%, and 11% respectively. Lila's total income from these investments is $9800. The income from the 11% investment exceeds the total income from the other two investments by $1200. Find how much Lila has invested at 11%.

Tasty Bakery sells three kinds of muffins: chocolate chip muffins at 40 cents each, oatmeal muffins at 45 cents each, and cranberry muffins at 50 cents each. Charles buys some of each kind and chooses twice as many cranberry muffins as chocolate chip muffins. If he spends $6.45 on 14 muffins, how many chocolate chip muffins did he buy?

Solve the following system. What is the value of y?

-5x - z = 2

x + 4y - 2z = 1

2x - 4y - z = -13

Solve the following system. What is the value of y?

-5x + 2z = 18

x + 4y + z = -25

-3x + 5y - z = -12

Solve the following system. What is the value of y?

-5x - z = 2

x + 4y - 2z = 1

2x - 4y - z = -13

Please help! I am so lost..