What is the complementary strand of dna for this strand of dna? actgctagctgactta?

Complementary strands of DNA have opposing matching nucleotides following base pair rules:

A -> T (U in RNA)
G -> C

With these in mind, let us copy your strand of DNA followed by the complementary strand underneath:

Original:                  A C T G C T A G C T G A C T T A

Complementary:  T G A C G A T C G A C T G A A T

This is the sequence for your complementary strand of DNA.