First, we have to calculate how much the original equal-payment was. Let us denote it by R, we have:

R \cdot \left(1 + \frac{0{,}15}{12}\right)^{-1} + R \cdot \left(1 + \frac{0{,}15}{12}\right)^{-2} + R \cdot \left(1 + \frac{0{,}15}{12}\right)^{-3} + R \cdot \left(1 + \frac{0{,}15}{12}\right)^{-4} + R \cdot \left(1 + \frac{0{,}15}{12}\right)^{-5} = 71

or

R \cdot \left(w^5 + w^4 + w^3 + w^2 + w\right) = 71

where w = \left(1 + \frac{0{,}15}{12}\right)^{-1} = 0{,}987654 Using the formula for adding terms of geometric progression, we get:

R \cdot \frac{w^6 - w}{w - 1} = 71 \quad \Rightarrow \quad R = 71 \cdot \frac{w - 1}{w^6 - w} = 14{,}7369

Therefore, the present value of the two already-done payments is:

R \cdot w + R \cdot w^2 = 14{,}7369 \cdot \left(0{,}987654 + (0{,}987654)^2\right) = 28{,}9302

So, the rest of the loan is 71-28,9302=42,0698. This amount is reduced by 25%, due to the government intervention. So, the new rest of the loan is:

42{,}0698 - 0{,}25 \cdot 42{,}0698 = 31{,}5523

This quantity must be repaid with six equal payments (denoted by H), starting the third month, with new annually interest rate equal to \tilde{r} = 18\% This means that:

H \cdot \left( s^3 + s^4 + s^5 + s^6 + s^7 + s^8 \right) = 31{,}5523

with:

s = \left(1 + \frac{0{,}18}{12}\right)^{-1} = 0{,}985222

Working as before, we get:

H \cdot \left( s^3 + s^4 + s^5 + s^6 + s^7 + s^8 \right) = H \cdot s^3 \cdot \left( 1 + s + s^2 + s^3 + s^4 + s^5 \right)

H \cdot s^3 \cdot \frac{s^6 - 1}{s - 1} = 31{,}5523 \quad \Rightarrow \quad H = 31{,}5523 \cdot \frac{s - 1}{s^9 - s^3} = 5{,}70561

This is the new monthly payment, upon request.