Look up "Everything You Need To Know About Math In One Big Fat Notebook pdf." It's the best thing I've ever been given, I have it with me in math class all the time and I've aced every test. I have it with me right now and it has everything I've ever been taught about math in it so it might help you.
Answer:
Katherine invested $12,000
Step-by-step explanation:
Use formula

where
I = interest,
P = principal,
r = rate (as decimal),
t = time (in years).
In your case,
t = 1 year,
r = 0.06 (or 6%)
P + I =$12,720, thus

Answer:
b = -7
Step-by-step explanation:
Answer:
b
c
a
d
Step-by-step explanation:
sum=addition
difference=subtraction
groups=hints multiplication
split into=division