Let 'c' represent the number of pictures Chelsea took.
Let 's' represent the number of pictures Sonya took.
For last year's Thanksgiving, c + s = 236
For this year's Thanksgiving, let 'x' represent the number of photos taken in total. x = c + s, where c and s are two integers that are the same (c = s).
And we know that for both years, c + s + x = 500.
As we know that c + s is already 236 from last year, we can remove c + s from the equation in bold and replace it with 236 instead.
236 + x = 500.
Now we have to isolate the x term.
x = 500 - 236
x = 264.
We know that x = c + s, where c and s are the same, so we can just use one of the variables and double it (so you either get 2c or 2s - it doesn't matter which one you pick because they're both the same).
2c = 264
c = 132
c = s
s = 132.
Both took 132 pictures this year.
