This is a math lesson on how to add four two-digit numbers by decomposing. The video begins with a review of decomposing numbers and the commutative property of addition. Then, the teacher presents a word problem about a farmer who picks different amounts of tomatoes each day and illustrates how to decompose the numbers into tens and ones to add them up, using mathematical reasoning and strategies such as combining like terms. The lesson concludes with a second word problem for practice and a summary of the key concepts learned.