It is true because if a is perpendicular to b and b is perpendicular to c therefore a has to be perpendicular to c also they said that all three lines are coplanar therefore the statement must be true
I hope this helped you out :)
Sum means to Add.
So the sum of d and 9 would be d + 9
Because she wanted to read instead of looking at the animals. Or the book was about the animals at the zoo.
10/4 I think
And simplified would be 5/2
