Answer:
Formular for the perimeter of a triangle:
[tex]perimeter = (side + side + side)[/tex]
let the first triangle to have perimeter, P
let the second triangle to have perimeter, P'
[tex]P = \{5 + (x - 5) + (x - 4) \} \\ P = \{(x + x) + (5 - 5 - 4) \} \\ { \underline{ P = 2x - 4}}[/tex]
and
[tex]P' = \{10 + 16 + (x - 10) \} \\ P' = \{x + (10 + 16 - 10) \} \\ P' = x + 16[/tex]
from the question, P = P'
therefore:
[tex]2x - 4 = x + 16 \\ 2x - x = 16 + 4 \\ { \boxed{ \boxed{x = 20}}}[/tex]
