Amaya has d dollars in her wallet. Lucy has $12 less than Amaya in her wallet.
Therefore Lucy have
in her wallet.
And we have to write an expression to show how much money both girls have altogether in simplest form. And for that, we have to add both total amount in there wallet. That is
The vertex is like the top point of the pyramid. If we cut in that direction, we essentially cut the pyramid in half. This makes a triangle crossection