Let F (X) = $2 ^ { 6 x }$ On the Interval [0,1]

Multiple Choice

Let f (x) = $2 ^ { 6 x }$ on the interval [0,1]. Let the interval be divided into three equal subintervals. Find the value of the Riemann sum $\sum _ { i = 1 } ^ { 3 } f \left( x _ { i } ^ { * } \right) \Delta x _ { i }$ if each $x _ { i } ^ { * }$ is the left endpoint of its subinterval.

A) $\frac { 13 } { 3 }$
B) 21
C) 7
D) 28
E) 8
F) 42
G) 14
H) 84