- Residual fitted
- normal Q
- scale location
- residual leverage graph.
Not able to interpret what it means.
Not able to interpret what it means.
The most obvious and important message is on the top left. When the predicted values (on the x axis) are larger than 40, the residuals are near zero, which is good. When they are smaller than 40, the residuals are systematically negative, meaning, these predictions are too high. Your simple linear model is not good for small values and you should seek to make your model a bit more complex, so smaller results become more accurate.
If you have an idea, what this means in terms of your question, try to model that idea. If not, try a quadratic term as @mkt said in the comments - or any other transformation (exponential, logarithmic, ...) that you have been taught.