Answer:
21
Step-by-step explanation:

Let the speed of the boat be x
so going against the current the speed is x-7
going with the current the speed is x+7
let the distance be d
time = distance / speed
time to go against the current = d/(x-7)
time to go with the current = d/(x+7)
time going against the current is 3 times going <span>with the current
</span>
d/(x-7) = 3d/(x+7)
⇒⇒⇒ divide by d
1/(x-7)
= 3/(x+7)
x+7
= 3(x-7)
x+7 = 3x - 21
2x = 28
x = 14
So, the speed of the boat in still water is = 14 mph
Me being a junior in high school and not knowing middle school math
Answer:
49
Step-by-step explanation:
Because there is a minus sign infront of x-3, we can convert x-3 into the negative form:
- * x
- * -3
-x + 3
Which gives us:
(-x + 3)(x + 11)
Now expand the brackets with the formula:
(a + b)(c + d) = ac + ad + bc + bd
-x * x = -x²
-x * 11 = -11x
3 * x = 3x
3 * 11 = 33
-x² - 11x + 3x + 33
-x² - 8x + 33
The formula for finding the x coordinate of a vertex in a quadratic equation is:
x = 
Plug known variables in:



Now, to find the y coordinate, plug this variable back into the quadratic equation:
-x² - 8x + 33

y = 49
So the y coordinate of the vertex is 49.
Hope this helps!
Answer: 140 m3
Step-by-step explanation:
Multiply the area of the trapezoid face by the length .
Since the area is 20, you multiply it by 7 to get 140