Question

BRAINLIEST ASAP! PLEASE HELP ME :)

Answer 1

Answer:

$\large \boxed{\text{3.0 mi/h}}$

Step-by-step explanation:

            Let x = the current of the river

Then 21 + x  = the speed going downstream (with the current)

  a nd 21 - x  = the speed going upstream (against the current)

Distance = speed × time

           d = st

            t = d/s

Time going downstream = time going upstream

$\begin{array}{rcll}\dfrac{2.4}{21+ x}& = & \dfrac{1.8}{21 - x} &\\\\2.4& = &(21 + x) \dfrac{1.8}{21 - x} &\text{Multiplied each side by (21 + x)}\\\\2.4(21 - x)& = & 1.8(21 + x) &\text{Multiplied each side by (21 - x)}\\50.4 - 2.4x&=& 37.8 + 1.8x&\text{Removed parentheses}\\50.4 & = & 37.8 + 4.2x & \text{Added 2.4x to each side}\\\end{array}$

$\begin{array}{rcll}12.6 & = & 4.2x & \text{Subtracted 37.8 from each side}\\x & = &\dfrac{12.6}{4.2}&\text{Divided each side by 4.2}\\\\ & = &\mathbf{3.0}& \text{Simplified}\\\\\end{array}\\\text{The current is \large \boxed{\textbf{3.0 mi/h}} }$

Check:

$\begin{array}{rcl}\dfrac{2.4}{21+ 3}& = & \dfrac{1.8}{21 - 3}\\\\\dfrac{2.4}{24}& = & \dfrac{1.8}{18}\\\\0.10 & = & 0.10\\\end{array}$

OK