I think this is right, i don't know for sure though. y=-x+(1)/(3)
15 = 5 + 8d - 12
15 = 8d - 7
15 + 7 = 8d
22 = 8d
d = 2.75
If b+2(a+1) = c, find the value of a+1
Subtract b from both sides: b+2(a+1) - b = c - b
2(a+1) = c - b
Divide both sides by 2:
a+1 = (c - b) /2
5(v-s)=30 and 3(v+s)=30
5v-5s=30
v-s=6
v=6+s now use this v in the second equation from the beginning...
3(6+s+s)=30
6+2s=10
2s=4
s=2 and since v-s=6, v=6+s=8
So the rate of the boat is 8mph and the rate of the current is 2mph