if your asking for the length of the third side, to find it first we have to build an equation.
let's take x as the length of the two sides with the same length. 
so your equation should be, 
x+x+2x-7=44cm 
=4x-7=44cm
 +7 +7
=4x=51cm
 ÷4 ÷4
=x=12.75cm
length of the sides with equal length= 12.75cm
length of the 3rd side= 12.75×2-7=18.5cm
check,
12.75cm+12.75cm+18.5cm=44cm
hope this helps.....