Question 343333
Let {{{A}}} and {{{B}}} be the unknown lengths,
{{{A+B+12=34}}}
{{{A=4B-3}}}
Substitute,
{{{4B-3+B+12=34}}}
{{{5B+9=34}}}
{{{5B=25}}}
{{{highlight(B=5)}}}
Then,
{{{A=4(5)-3}}}
{{{A=20-3}}}
{{{highlight(A=17)}}}