Joelle has $15.75. she spent $6.38 at the store.

which equation can be used to represent how much money, x, joelle has left?

x + 15.75 = 6.38

x + 6.38 = 15.75

x−6.38=15.75x−6.38=15.75

6.38x = 15.75

X + 6.38 = 15.75 would be the answer 
      x=9.37
for the first option, you are not adding 15.75 and x together. 
for the second option, it is correct, because in the problem, it is giving the operation, 15.75-6.38=x. when you turn it do inverse operation, you get x + 6.38 = 15.75. 
for the third option, it doesn't make sense and it's not doing what the problem is asking for.
for the fourth option, you are not multiplying. you are subtracting 15.75 by 6.38 to get x.

How many groups are there?