R+S = P
R+S = P
The key to this problem is using inverse operations to get m by itself. (If you don't recall, inverse operations "undo" each other. Like + and -, or x and /.)
A tip to remember: when solving for a variable in the denominator, like your m, it is always helpful to get it in the numerator.
So to begin!
The problem is being divided by m, so to move it to the numerator you want to multiply both sides of the equation by m. Remember, keep the equation equal by doing the same operation to each side.
It should look like this: m * (R + S)/(mn) = m * P
That will give you: (R + S)/n = mP
Notice the m's on the left "cancel" each other out. And you're actually almost done! We need to get m by itself and get rid of the P. m and P are multiplied together, so to undo that, you should divide by P.
Should look like: (R + S)/n /P = mP /P
Now the P's on the right cancel, and you are left with: (R + S)/n /P = m
To make it look a little better: notice you are dividing R + S by both n and P. So we can put both n and P in the denominator of the fraction.
Final answer: (R + S)/(np) = m
First cross multiply Pmn = R + S
Finally divide both sides by Pn to get m = (R + S)/Pn
I usually circle the variable I am trying to solve for in each step, then use algebraic principles on both sides of the equation to isolate that variable