m and n are the x and y coordinates, respectively, of a point in the coordinate plane. If the points (m, n) and (m + p, n + 21) both lie on the line defined by the equation x = (y/7) - (2/5), what is the value of p?
Options.
A) 1  B) 2  C) 3  D) 4  E) 5
x = (y/7) - (2/5), and so y = 7x + 14/5. The slope is 7.   (n+21-n) / (m+p-m) = 7   p = 3   The answer is 3.
<result>C</result>
m and n are the x and y coordinates, respectively, of a point in the coordinate plane. If the points (m, n) and (m + p, n + 21) both lie on the line defined by the equation x = (y/7) - (2/5), what is the value of p?