Isolate y first;
y+2=3(x-7)
y+2=3x-21
y=3x-21-2
y=3x-23
The slope here would the coefficient of x and the y intercept is the constant number.
Slope is 3, y-intercept is -23.
The solution could either be a or c.
To check, insert 7 as an x value and see the y value.
y=3(7)-23
y=-2
Therefore the point (7, -2) falls on the line. The correct solution is a.
Hope I helped :)