A boat can go 45 mph in still water It takes as long to go 6

A boat can go 45 mph in still water. It takes as long to go 630 miles upstream as it does to go downstream 720 miles. How fast is the current?

Solution

D=RT
630=(45-C)T
T=630/(45-C)
720=(45+C)T
T=720/(45+C) BECAUSE THE 2 TIMES ARE THE SAME SET THE 2 EQUATIONS EQUAL & SOLVE FOR C (THE CURRENT).
630/(45-C)=720/(45+C) CROSS MULTIPLY.
720(45-C)=630(45+C)
32,400-720C=28,350+630C
-720C-630C=28,350-32,400
-1,350C=-4,050
C=-4,050/-1,350
C=3 MPH. IS THE SPEED OF THE CURRENT.
PROOF:
630/(45-3)=720/(45+3)
630/42=720/48
15=15