y = negative 13 over 10x + 13 is the best choice. (0, 13) is the y-intercept. If we begin at (0, 13) and move approximately 10 units to the right, y decreases by 13, so the slope is m = -13/10.
Writing y = negative 13 over 10x + 13 as y = negative 13 over 10 plus 13 would be clearer. We must emphasize that the slope is -13/10 and that this should be enclosed in parentheses: y = (negative 13 over 10)x + 13.
