2x(-5x-3)
2x(-5x)= -10x and 2x(-3)= -6x
= -10x sq - 6x
-10x is sq bc you are multiplying the same variable twice
Given that I no not see any explanation in the previos answer, I think you can benefit of this.
Exothermic refers only to the fact that the reaction releases energy in the form of heat when occurs. So, the enthalpy is higher at start and lower and the end.
Seen in this way, you can deduct that the change in enthalpy is negative, which is what the third option says.
Consider the number as 'n' (for now)
3n - 9 = 69
3n = 69 + 9
3n = 78
n = 78/3
n = 26
Therefore, The number is 26
15 gallons
hope this helps. not really sure what you mean by that.
