Number of years before buying the house (n) = 36 -18 = 18 years
Yearly increase of house value (i) = 6% = 0.06
After 18 years,
The house value = (1+i)^n = (1+0.06)^18 = 2.85 the current value.
Additionally,
Increase in rate = (2.85-1)/2.85 = 0.6491 ≈ 0.65 = 65%. This is the discount rate for today's price. In other words, if the house is bought today, it will be paid for 65% less the price after 18 years.