Required Answer :
Total length of string = 30'
According to the figure,
[tex] \quad \twoheadrightarrow\sf { 30' = 15' + A + 9' } \\ [/tex]
[tex] \quad \twoheadrightarrow\sf { 30' = 24' + A} \\ [/tex]
[tex] \quad \twoheadrightarrow\sf { 30' - 24' = A} \\ [/tex]
[tex] \quad \twoheadrightarrow\underline{\boxed{\sf { 6' = A}}} \\ [/tex]
Therefore, the missing dimension in the dimension strings is 6'.
