A 13 Mile Walkathon Has Three Checkpoints $4 \frac { 1 } { 7 }$

A 13 mile walkathon has three checkpoints. The first is $4 \frac { 1 } { 7 }$ miles from the starting point. The second checkpoint is $5 \frac { 3 } { 8 }$ miles from the first.
a. How many miles is it from the starting point to the second checkpoint?
b. How many miles is it from the second checkpoint to the finish line?

A) (a) $9 \frac { 29 } { 112 }$ miles; (b) $3 \frac { 27 } { 56 }$ miles
B) (a) $9 \frac { 29 } { 56 }$ miles; (b) $4 \frac { 27 } { 56 }$ miles
C) (a) $9 \frac { 29 } { 112 }$ miles; (b) $4 \frac { 27 } { 112 }$ miles
D) (a) $9 \frac { 29 } { 56 }$ miles; (b) $3 \frac { 27 } { 56 }$ miles
E) (a) $9 \frac { 29 } { 56 }$ miles; (b) $4 \frac { 27 } { 112 }$ miles