You get everything you need from factoring the last expression:
The left side is a difference of squares, and we get another difference of squares upon factoring. We end up with
Plug in everything you know and solve for 
:
2|3x + 5| = -10 . Divide both sides by 2:
|3x + 5| = -5 ===>3x+5=-5 & -3x-5=-5 In both cases x=0
Equilateral correctly describes pentagon
Alright, so we'd use the combinations with repetition formula, so we choose from 4 schools to distribute to and distribute 8 blackboards. It's then
( 8+4-1)!/8!(4-1)!=11!/(3!*8!)=165
For at least one blackboard, we first distribute 1 to each school and then have 4 blackboards left, getting (4+4-1)!/4!(4-1)!=7!/(4!*3!)=35
You will need:
(2240/625)*250=896 ml of treatment liquid.
If each bottle contains 250 ml you'll need 3.6 bottles (3 bottles and a bit more than half a bottle).
I do not think you need the conversion 1 cubic meter=1000 litres unless the volume of the tank is in cubic meters BUT 2240 cubic meters seems too large!
