Answer
4 ft
Work Step by Step
Let m be the length of the middle part of the table. Let l be the length of a leaf.
$m+l=5.5$
$m+2l=7$
Multiply the first equation by -1, and add the equations to eliminate m.
$m+\ \ l=5.5\ \ \ \ \ $ multiply by -1$\ \ \ \ -m-\ \ l=-5.5$
$m+2l=7\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \underline{m+2l=\ \ \ 7}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ l=1.5$
Substitute 1.5 for l in either equation to solve for m.
$m+l=5.5$
$m+1.5=5.5$
$m+1.5-1.5=5.5-1.5$
$m=4$
