Divide 33 photos into 2 groups so the ratio is 4 to 7

First you'll need two equations ( you can use any variables you want)
A= photo group 1
B= photo group 2
First equation:
A + B = 33
This is because the total number of photos from both groups is 33
Second equation:
4A = 7B
This is because the ratio is 4:7 so for every four photos in group A there must be 7 photons in group B.
Then take the first equation A + B = 33 and subtract B from both sides. Making the equation A = 33 - B
Then with that equation, substitute it in for equation 2 and it will look like this. 4(33-B) = 7B
Then distribute the 4 to the 33 and the -B making the equation 132 - 4B = 7B
Then add 4B to each side
Making the equation 132 = 11B
Then to get B by itself you must divide each side by 11 making the equation 132/11 = B which simplifies to 12 = B
Then plug in 12 for B in the first equation like this A + 12 = 33
Then subtract 12 on each side of the equation to isolate A so A = 21

So
A = 21
B = 12