I'm not sure what they mean by diagram, but to get percentages in decimal form, you just divide the percentage value by 100 (move the decimal point back 2 places).
For example:
22% -> 22/100 = .22
65% -> 65/100 = .65
2% -> 2/100 = .02
So to get a percentage of a quantity (which is 250 in this case), you multiply that quantity by that decimal version of the percentage.
To get the decimal version of 270%, divide 270 by 100:
270/100 = 2.7 (the decimal point was just moved back 2 places)
So 270% of 250 is just the quantity (250) times the percentage (2.7):
250 * 2.7 = 675