My assignment:
Querido Dr. Peterson:
Es un verdadero honor para nosotros que haya contestado a nuestra carta.
Agradecemos enormemente sus observaciones y entendemos que en nuestra carta, por no extendernos demasiado, no nos hemos explicado con suficiente claridad.
Si le parece bien le contestaremos a sus observaciones una a una:
and my attempt:
Dear Dr. Peterson,
it is a truly honor for us that you have answered to our letter.
We greatly appreciate your observations and we understand that in our letter we have not explained clearly enough, because we only present main ideas.
Considering your observations, we will answer to them one by one:
I don't know why but it sounds horrible to me. Please, help.