Steepness is the <em>absolute value</em> of a slope. (The sign of a slope determines the direction of the incline: negative slope corresponds to pointing up to the left, positive slope points up to the right.)
So it is only the absolute value of a slope that should be used in any comparison. Because of that, one cannot, in general, say that negative slopes are steeper than positive slopes.
A higher positive slope means a steeper upward tilt to the curve, which you can see at higher output levels. A negative slope that is larger in absolute value (that is, more negative) means a steeper downward tilt to the line.
So you basically, just make it a ratio. Since a percentage is out of 100, just make the 5 into 100. To get 5 to 100, you times 20. Then you do the same thing to the 4 which you get 80.
