Question

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Answer 1

let DF become y

y = x + 9

to find x let y = 0

0 = x + 9

transpose 9

-9 = x

therefore DF = -9 as an integer

Answer 2

DE+EF=DF
8x+2=x+9
8x-x=9-2
7x=7
x=7/7
x=1

DF=x+9
put the value of x
DF=1+9
DF=10