We need to know the calculation formula of percentage. The percentage increase of numbers can be expressed by mathematical formula. Percentage increase = (new price-old price) ÷ old price × 100%. This formula tells us how to calculate the percentage increase of a number.

Substitute the new price = 13 and the old price =9 into the above formula to get the answer. The calculation result shows that the number of blocks has increased from 9 to 13, an increase of 44.44%.