This is because the 3 is distributed to the 4 to get 12. The 10^4 is distributed to the 10^23 and because of the exponent laws, the exponents are added to get 27 and the 10's (being the base) is left alone.
The first one simplifies by collecting like terms to become: 7a²(4b²+9ab+10) and the second one simplifies again by collecting like terms to become: 7u(16u²-49v²) Got anymore questions, happy to help :)
