This equation has infinitely many solutions, since you can pick any value for x and solve for y...and vice versa. The graph of all these solutions will be a straight line.
Maybe you want the equation of this line in slope-intercept form:
( y + 7 ) + x = 57
y + 7 = -x + 57
y = -x + 57 - 7
y = -x + 50