Differentiating:
Now you have to do a bit of algebra to isolate y' but it should be doable. Collect all the terms with y' on one side and everything else on the other. Factor out y' and you should be good. Then plug in (1,4) to your end result.
I've had so many answers... lets just say for arguements sake .4017475548, which is no way the answer.
Ive had answers like that, negative answers, answers like 6.2, 5.45, etc