Answer: C
M76.61 is the correct code because it is used to code for Achilles tendinitis in the right leg which is the diagnosis here.
Option A is not correct because M76.51 is used to specify patellar tendinitis in the right knee which is not the diagnosis here.
Option B is not correct because M76.01 is used to specify Gluteal tendinitis of the right hip which is not the diagnosis here.
Option D is not correct because M76.12 is used to specify psoas tendinitis of the left hip which is not the diagnosis here.