Answer :
Just take out the s' to make it easier
So 9-5+2-1
9-5= 4
4+2=6
And then +1 is 7
And all you have to do is put the s back in so the answer is:
7s
So 9-5+2-1
9-5= 4
4+2=6
And then +1 is 7
And all you have to do is put the s back in so the answer is:
7s