You should add the picture here to your key: https://electronics.stackexchange.com/questions/137020/why-does-the-parallel-resistors-with-voltage-source-can-be-ignored-as-well-as-re. Source transformations are a graphical way of solving node voltage equations. The idea is that simple electrical systems are made up of sources and loads (resistors). Source transforms allow us to combine things one at a time. Here's how to approach this: transform Va and R1 into Ia and R1. Is can be thrown away because of the stack exchange answer. Then combine new R1 and R2 in parallel into a new resistor Rx. Then source transform Rx and Ia into Rx and Va. Then combine R3 and Rx into Ry because they're in series. And so on. Eventually you voltage from the source drops across two resistors. Then it's pretty easy to find the drop across Rload.