It sounds like you are describing the equation of a line in slope-intercept form, which is given by the equation:
\[ y = mx + b \]
where \( m \) is the slope and \( b \) is the y-intercept.
Given your values:
- Slope \( m = -\frac{3}{4} \)
- Y-intercept \( b = 3 \)
The equation of the line would be:
\[ y = -\frac{3}{4}x + 3 \]
This represents a line that decreases as \( x \) increases, starting at the point (0, 3) on the y-axis. If you need any further analysis or graphing of this line, feel free to ask!