Answer:
11.58%
Step-by-step explanation:
The initial volume if blood flowing through the artery is given by

To achieve a new volume of 155% (55% increase) of the initial volume, the new radius must be:
![V'= 1.55V\\1.55V=k(r')^4\\1.55kr^4 = k(r')^4\\(\sqrt[4]{1.55}*r)^4=(r')^4 \\(1.1158*r)^4=(r')^4 \\r'=1.1158*r](https://tex.z-dn.net/?f=V%27%3D%201.55V%5C%5C1.55V%3Dk%28r%27%29%5E4%5C%5C1.55kr%5E4%20%3D%20k%28r%27%29%5E4%5C%5C%28%5Csqrt%5B4%5D%7B1.55%7D%2Ar%29%5E4%3D%28r%27%29%5E4%20%5C%5C%281.1158%2Ar%29%5E4%3D%28r%27%29%5E4%20%5C%5Cr%27%3D1.1158%2Ar)
Since the new radius is 1.1158 times larger than the initial radius, the percentage increased is:

The diagonals would be perpendicular (intersect at a 90* angle)
15.6 in 13 minutes? are you asking how it got to 15.6 in 13 minutes?