What is the equation of the line that passes through the point (1,4) and has a slope of 3

You want to find the equation for a line that passes through the point (1,4) and has a slope of 3.
First of all, remember what the equation of a line is:

y = mx+b
Where:
m is the slope, and
b is the y-intercept
To start, you know what m is; it's just the slope, which you said was 3. So you can right away fill in the equation for a line somewhat to read:
y=3x+b.
Now, what about b, the y-intercept?

To find b, think about what your (x,y) point means:
(1,4). When x of the line is 1, y of the line must be 4.