The function f is such that, for every integer $n$
$$\int _ { n } ^ { n + 1 } \mathrm { f } ( x ) \mathrm { d } x = n + 1$$
Evaluate
$$\sum _ { r = 1 } ^ { 8 } \left( \int _ { 0 } ^ { r } \mathrm { f } ( x ) \mathrm { d } x \right)$$
A 36
B 84
C 120
D 165
E 204
F 288