Answer : The equation could you use to find p is, 
Step-by-step explanation :
Let the cost of 1 pen be, 'x'
and the cost of 1 pencil is, 'p'
As we are given that total cost of 1 pen and 1 pencil is $2.10. The equation will be:
............(1)
And we have also given that the pen costs twice as much as a pencil. The equation will be:
............(2)
Now put the equation 2 in equation 1, we get:


Thus, the equation could you use to find p is, 
The x coordinates signs change.
Answer:
m=-4
Step-by-step explanation:
5m-10m=-10m+5m=-(10m-5m)=-5m=20
divide by 5 on both sides, -m=4
miltiply by -1 on both sides, m=-4
Answer:
Step-by-step explanation:
3*n*p*6 = 18np