Can somebody answer this for me?

Given: passes though (6,3) and m=(5/3).
Ok so we know that y = mx + b is the equation of a line and we have m and we can find b via substitution.
y = mx + b
3 = (5/3)(6) + b
3 - (5/3)(6) = b
b = -7
Great now we know b so we can construct the rest of the linear function.
y = f(x) = (5/3)(x) - 7
You can always check the answer by plugging 6 into the x variable.
f(6) = (5/3)(6) - 7 = 3
(6,3) checks out.