If my understanding is correct, it should be like this:

Suppose that after n years, the income just pays off the principal and interest.

Total loan principal and interest =1000+1000 * (1+5%) n ...................1formula.

The income of the nth year = 200 * (1+40) (n- 1) ..............................................................................................................................

1 equation =2 equation can solve n.

Of course, this formula is difficult to understand, and it has to be interpolated.

We simplify the formula and get 5 = (1.4) (n-1)-(1.05) n.

Let y = (1.4) (n-1)-(1.05) n, then data can be obtained as long as y is equal to zero.

When n=5

y=-2.5

When n=7.

y=0.494

When n=6

y=- 1.32

So the value of y=0 is between 6 and 7.

Therefore, in the seventh year, the enterprise can pay off the principal and interest with the income of that year for the first time.

I hope it works for you. Type so many words. If the calculation is correct, add more.