At what rate must the current be to changed to produce 40V emf

[mr_coffee]

A 20 H inductor carries a steady current of 4.0 A. At what rate must the current be changed to produce a 40 V emf in the inductor?

I odn't get this one because it gives you all the information!
The formula is:
EMF = -L di/dt
they want u to find di/dt, but they already give you it has a steady current of 4.0A, so isn't di/dt just i, which is 4.0A?
Then the EMF would be 40, and they say L = 20H, so I'm stuck on what intermediate step I'm missing! thanks

 

[Integral]

For a steady current, at any value,

$$\frac {dI} {dt} = 0$$

 

[mr_coffee]

So basically, I can disregard that they told me it had a steady current of 4.0A right? and then just use
di/dt = EMF/-L to find the di/dt?

 

[mr_coffee]

thanks that was the trick! i did that the last time, but forgot the minus sign!