4. The product of square roots is the square root of the product, so square root of 7 times square root of 3 is the same as square root of 7*3. The answer is 5*3*sqrt(21)=15sqrt(21)=68.74 approx.
5. Sqrt(6)*sqrt(6)=6, so answer is 4*2*6=48.
6. 6x.
7. 5y.
8. sqrt(3)*sqrt(12)=sqrt(36)=6. z^12*z^3=z^15. Answer: -18*6*z^15=-108z^15.
9. Expand the brackets: (2sqrt(3)*(3sqrt(3))+(2sqrt(3)(sqrt(2))-(sqrt(2))(3sqrt(3))-2=
(6*3)+2sqrt(6)-3sqrt(6)-2=(18-2)-sqrt(6)=16-sqrt(6)=13.55 approx.
10. 2*5+4sqrt(15)-2sqrt(15)-12=2sqrt(15)-2=5.75 approx.