Write the equation in standard form: 3x-9=7y

If in standard form you mean slope intercept form, then you are looking to create an equation that looks like this:

y = mx + b

So you need to move around the numbers whilst keeping both sides equivalent.

3x - 9 = 7y
7y = 3x - 9
y = (3x)/7 - 9/7

Your answer should look like this:

y = (3x)/7 - 9/7

If this is not what you meant by standard form please comment and I will see if I can adjust the answer.