There are a total of 10 women and 3 men. Let's define two variables:
w: land inherited by a woman
m: land inherited by a man
Given that they inherited a 30000 (square miles) of land and that each brother has inherited double what each sister has inherited, we can establish the next equations:
2*w = m
10*w + 3*m = 30000
Replacing the first equation into the second one, and solving for w:
10*w + 3*2*w = 30000
16*w = 30000
w = 30000/16
w = 1875 square miles
Your mom, and all of her sisters, inherited 1875 square miles each
