Respuesta :

see the picture to better understand the problem

F________G_______H_______I

we know that
FI=FG+GH+HI-----> solve for GH
GH=FI-FG-HI
FI=7 units
FG=2 units
HI=1 unit
substitute
GH=7-2-1-----> GH=4 units

the answer is
GH=4 units