you should probably read something like
this. operators all have a precedence - some get done before others, just like in math.
If i recall correctly, anything inside parens is done first, so we'd get
6*10/5*5+14/2-9+20
Then, mult/div come next, in order from left to right
60/5*5+14/2-9+20
60/5*5+14/2-9+20
12*5+14/2-9+20
60+14/2-9+20
60+7-9+20
then, addition and subtraction, in order from left to right
67-9+20
58+ 20
78
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors