This question is worded badly, so don't be alarmed.
Obviously if this were a square patter the number of red tiles could only be 1,4,9,16,25,36 etc and this is not the numbers given...It would help tremendously if they gave you another reference point so as to know how the tiles were being laid out.
If they are laid out alongside one another with a consistent border for each you wouldn't need 12 blue tiles for each red tile either...if two were laid side by side you would only need 20 blue tiles to have the border around both...you see how the arrangement makes a huge difference and you are given no details as to what that arrangement is...
So just to keep it simple, assume that each red tile is surrounded by 12 blue tiles....
Total tiles equals r+12r=13r
t=13r so
t(15)=195, t(20)=260, t(25)=325, t(30)=390
The answer is 5.1 when you enter it into a calculator :)
Distance around a circle is CIRCUMFERENCE
DIAMETER*PI=CIRCUMFERENCE
