Question

the difference of one more than six times a number and four more than three times the same number, using numbers 3, 5 and 7.

Answer 1

6x+1-3x+4=
6(3)+1-3(3)+4=
19-9+4=
19-13=6

Answer 2

I think you meant
(6x+1)-(3x+4) = 6x+1-3x-4 = 3x-3
using 3: 3(3)-3 = 6


Yiur asnwer was right, but your grouping of values without parentheses was wrong. As it was written, you'd have

6(3)+1-3(3)+4
multiplication comes first, unless otherwise specified using parentheses:
18+1-9+4
The addition and subtraction are done left to right:
19-9+4
10+4
14

Answer 3

1+1