To solve this problem, let's assume that the first part of the amount lent is x and the second part is y.

According to the given information:
1) The sum of the two parts is Rs 4000, so we have the equation x + y = 4000.

2) The interest received at the end of the year is Rs 400. We can calculate the interest for each part using the formula: Simple Interest = (Principal * Rate * Time) / 100.

The interest for the first part is (x * 8 * 1) / 100 = 8x/100.
The interest for the second part is (y * 12 * 1) / 100 = 12y/100.
So we have the equation 8x/100 + 12y/100 = 400.

To solve these two equations, we can use the method of substitution or elimination. In this case, let's use the elimination method:

Multiplying the first equation by 8, we get 8x + 8y = 32000.
Multiplying the second equation by 25, we get 25x + 30y = 10000.

Now, subtracting the equations, we have:
(8x + 8y) - (25x + 30y) = 32000 - 10000
-17x - 22y = -22000

Simplifying this equation, we get:
17x + 22y = 22000

Now, let's multiply the first equation by 17:
17x + 17y = 68000

Subtracting this equation from the previous one, we have:
(17x + 22y) - (17x + 17y) = 22000 - 68000
5y = -46000

Dividing both sides by 5, we get:
y = -46000/5
y = -9200

Since the amount lent cannot be negative, we discard this solution.

Now, let's try another approach. Let's assume that the first part of the amount lent is y and the second part is x.

Using the same two equations:
x + y = 4000
12x/100 + 8y/100 = 400

Multiplying the first equation by 8, we get:
8x + 8y = 32000

Subtracting this equation from the second equation, we have:
(12x/100 + 8y/100) - (8x + 8y) = 400 - 32000
4x/100 = -31600

Multiplying both sides by 100, we get:
4x = -31600 * 100
4x = -3160000

Dividing both sides by 4, we get:
x = -3160000/4
x = -790000

Again, we have a negative value for the amount lent, which is not possible.

Therefore, there must be an error in the question or the given options. None of the options provided (a, b, c, d, e) are correct.