LC Circuit Problem Homework: Calculate Values of L & R

[Am_o]

Homework Statement

When the current in the portion of the circuit shown in the figure below is 4.00 A and increases at a rate of 0.500 A/s, the measured voltage is ∆ = 15.0 V. When the current is 4.00 A and decreases at the rate of 0.500 A/s, the measured voltage is ∆ = 10.0 V. Calculate the values of (a) L and (b) R.

Homework Equations

Given formula sheet.[/B]

The Attempt at a Solution

My attempt:
I was given an equation:
adding flux formula:
i=Imax(1-e^-t/Γ)
Γ=L/R ---> Γ=L/(V/I)----> Γ=LI/V
R=V/IAm I on the right track?

 

[cnh1995]

Voltage between points a and b is sum of inductor voltage and resistor voltage. Inductor voltage is Ldi/dt..

 

[Am_o]

So what I do is:
Vt=Vr+VL
Vr= I*R
VL= -L(di/st)
∴ Vt=(I*R)+(-Ldi/dt)

So put in the variables given:
15v=(4A*R)+(-L(0.5A/s)) increasing rate
10v=(4A*R)+(-L(-0.5A/s)) decreasing rate
Then solve for L & R like?

 

[NascentOxygen]

So what I do is:
Vt=Vr+VL
Vr= I*R
VL= -L(di/st)
∴ Vt=(I*R)+(-Ldi/dt)

So put in the variables given:

Hi Am_0.

That's the right idea. Except there should not be a negative sign in the expression for V_L.

Also, where you are asked to provide all relevant equations in your homework post, please only include those relevant to the problem at hand.