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Notice that everything is being multiplied. Therefore by the law of exponents, we are able to add the exponents for common bases. Let's deal with 1 variable at a time.

Step 1: Let's look at the x's

-x * x^2

This is the same as

-x^(1+2)

-x^3

Step 2: Let's look at the y's

y^6 * y

This is the same as

y^(6+1)

y^7.

Therefore we see 4(-x^3y^7). Then you just multiply the four to the whole thing.

-4x^3y^7.

Please let me know if you need any clarification. I'm always happy to answer your questions.