I am having some trouble understanding this solution to a question which required the elimination method. It comes from page 266 of Head First Algebra.
On the right hand side why does the + 0.4p become -0.6p on the next line?
I understand everything else, even the cancelling out parts I think.
Thank you.
Notice how the entire first equation is multiplied by $-1$, turning the system into $$\begin{align} -c-p&=-5 \\ c+0.4p&=2.6 \end{align}$$ Those two equations are then added together to produce $$\require{cancel}\cancel{c-c}-p+0.4p=-2.4$$ which simplifies to $$p(-1+0.4)=-2.4 \implies -0.6p=-2.4$$