John Gill Commentary 2 Kings 10:7

"And it came to pass, when the letter came to them, that they took the king`s sons, and slew them, even seventy persons, and put their heads in baskets, and sent them unto him to Jezreel." — 2 Kings 10:7 (ASV)

And it came to pass, when the letter came to them
They did not in the least hesitate, but immediately complied with the contents of it:

that they took the king's sons, and slew seventy persons ;
which was the whole number of them:

and put their heads in baskets, and sent them to Jezreel ;
as a present to Jehu, just as they carried the firstfruits, as Abarbinel observes.