im assuming that square A and C are identical. therefore, they have the same sidelengths and since their sidelengths add to 16, each square must have sidelength 8. now the total length of tape used to mark square A is the perimeter of square A which is 8 + 8 + 8+ 8 = 32. we know each side is 8 cause it's a square and squares have equal sides of equal lengths.
let me know if you have any questions!!!