A boat makes a 120-mile trip downstream in 3 hours but makes the return trip in 4 hours. What is the rate of the current?3 mph 4 mph5 mph

With the current 40 miles per hour
Against the current 30 miles per hour
bv means boat velocity with NO current
cv means current velocity
A) bv + cv = 40 mph
B) bv - cv = 30 mph
Adding both equations:
2bv = 70
boat velocity with NO CURRENT = 35 miles per hour

Using equationA
bv + cv = 40
35 + cv = 40

current velocity = 5 miles per hour