Answer:
The correct option is 3.
Step-by-step explanation:
Given: [tex]\overline {PQ}\cong \overline{QR}[/tex], [tex]PQ=3x-1,QR=26[/tex].
Prove: [tex]x=9[/tex]
[tex]\overline {PQ}\cong \overline{QR}[/tex] (Given)
[tex]PQ=QR[/tex] (Segment congruent postulate)
[tex]3x-1=26[/tex] (Substitution property of equality)
Add 1 on both sides.
[tex]3x-1+1=26+1[/tex] (Addition property of equality)
[tex]3x=27[/tex]
Divide both sides by 3.
[tex]x=9[/tex] (Division property of equality)
Hence proved.
The required equation for box 1 is 3x=27.
Therefore the correct option is 3.