If RBC's are lacking mitochondria then from where do they get ATP's to generate energy

Red blood cells differ in many ways from other cell types in the body. One of the major differences is that they do not contain mitochondria, a critical organelle that typically is responsible for generating the majority of cellular ATP, in animal cells, through a process known as oxidative phosphorylation. Because of this, red blood cells generate ATP through an anaerobic process known as glycolysis. This multistep process starts when red blood cells take up glucose, through facilitated transport. Following this uptake, the cell starts a very detailed and intricate multi-step process via the investment of two ATP molecules, to eventually generate 4 total ATP molecules, leading to a net gain of 2 ATP molecules for each glucose used.

This method is actually very inefficient for generating energy, as mitochondria are able to generate up to 34 additional ATP from one glucose molecule following glycolysis in typical cells. However, by generating ATP in this way, red blood cells are able to carry out their primary function of carrying and delivering oxygen throughout the body without using it for energy generation, allowing them to function much more efficiently. Hope this helps!