Manuel earns $42.94 walking his neighbor's dog. he puts half the money in a savings account. the rest he keeps for spending money. then, he spends $11.13 on a new book. how much spending money does manuel now have?

The solution is simple:
We know Manuel decided to walk the neighbors dog for $42.94. This is a problem assuming he only walked it once. He put HALF of the cash in a savings account, and kept the other half to spend on whatever he wants. That means we take $42.94 and divide it by 2 in order to find out how much went into the savings account, and how much he kept.
42.94/2=21.47
We now know that he kept $21.47, and he put the other $21.47 into a savings account. Ok, now forget about the savings account and the money in it. 
We know he spends $11.13 of his $21.47. We simply subtract now to find out how much he has left
$21.47-11.13=10.34
Manuel has $10.34 of spending money left.
~Hope this helps!