Step-by-step explanation:
We have three sides: 7 + 4 + 10 = 21
we need to find the fourth side, using Pythagorean theorem, and add it.
a^2 + b^2 = c^2
a = 10 - 7 = 3
b = 4
so 3^2 + 4^2 = c^2
9 + 16 = c^2
25 = c^2
5 = c
We add them together: 5 + 21 = 26