51/4 + 8/14 can somebody me simplify the answer

So first convert to common denomenator( bottom number)
'
4 and 14
find least common multiple
factor
4=2 times 2
14=2 times 7
Least Common Multiple=2 times 2 times 7=28

1/4 times 7/7=7/28
8/14 times 2/2=16/28
add
5 1/4+8/14=5+1/4+8/14=5+7/28+16/28=5+23/28

the answer is 5 23/28

V - the crew rowing rate,
u - rate of the current.
Downstream:  v + u = 13.5/1.5 = 9 mph
Upstream :      v - u = 13.5/4.5 = 3 mph
u = 9 - v
v - ( 9 - v ) = 3
v - 9 + v = 3
2 v = 12
v = 6 mph,   u = 9 - 6 = 3 mph
the crew`s rowing rate is 6 mph and the rate of the current is 3 mph.