Basic solving for fractions Can someone help me with this? I am a beginner to physics and in a question i need no isolate a constant to solve for another one.

A/B=C/D solve for D step by step please.
We start with $\frac{A}{B}=\frac{C}{D}$. 

Our goal is to isolate $D$. (Of course since $B$ and $D$ are in the denominator, they are assumed to be non-zero).

First we want to get $D$ into the numerator. We multiply both sides by $D$. 

$\frac{AD}{B}=C$

Now we multiply both sides by $B$.

$AD=BC$.

Lastly, we divide both sides by $A$ (once again, this assumes that $A$ is non-zero).

We get that $D=\frac{BC}{A}$
We start with $\frac{A}{B}=\frac{C}{D}$. 

Our goal is to isolate $D$. (Of course since $B$ and $D$ are in the denominator, they are assumed to be non-zero).

First we want to get $D$ into the numerator. We multiply both sides by $D$. 

$\frac{AD}{B}=C$

Now we multiply both sides by $B$.

$AD=BC$.

Lastly, we divide both sides by $A$ (once again, this assumes that $A$ is non-zero).

We get that $D=\frac{BC}{A}$