difference of a number divided 7 by and 6 equals 3
Your question has some typos I think ("divided 7 by?") I'll do a best guess.
"Difference" means subtraction.
"a number" is another way of saying a variable, or x in this case.
"divided by" is indicating division, or a fraction in this case.
"equals" is saying the whole thing equals 4
altogether
x/6 - x/7 = 3
Also it's ambiguous which number is subtract the other.
Hopefully my interpretation is what was intended by the teacher.
I hope you can do that math, but if you can't lets try together:
x/6 - x/7 = 3
(7x-6x)/6*7 = 3
x = 3*42
x = 126