The length of DF is B) 6 cm
What we already know is that ABC is congruent to DEF. Knowing this information we can use CPCTC theorem to prove that AC is congruent to DF. And Since we know that AC is 6 cm, DF must then be 6 cm.
CPCTC is short for "corresponding parts of congruent triangles are congruent" theorem. This pretty much states that if triangles are congruent then their individual corresponding parts must also be congruent. So corresponding sides will be congruent and corresponding angles will be congruent.
Hope this Helped, and Good Luck!
