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