Ples ! need answers for 12- answer for brainlest answer and ! :

Find the solution of system of equation y= x-4 y=4x+2

9/10 divide by -3/15 as a mixed number

Which of the following would be a reasonable estimate for the weight of a pencil? a. 1 × 10^-20 lb b. 1 × 10^20 lb c. 1 × 10^2 lb d. 1 × 10^-2 lb