Step-by-step explanation
Let's recall the framework of the equation of a line:
We say that two lines are perpendicular if the slope of one line is minus the multiplicative inverse of the slope of the other one; mathematically, this amounts to the following equation:
In this case, the slope of our line is 4/7. Then the slope (m) of any line perpendicular to it must satisfy
Solving this equation for m, we get
Answer
The answer is 2.