Write the equation of the line that passes through the points (1, 7) and (5, 15) using function notation.
y = 2x + 5
y = 4x + 8
f(x) = 2x + 5
f(x) = 4x + 8
y = 2x + 5
y = 4x + 8
f(x) = 2x + 5
f(x) = 4x + 8