The y intercept in a regression line is the point where the line of best fit meets the y axis. It is the expected mean value of y when x=0.
In the given graph, x cooridnate represents the amount of fertilisers and the y coordinate represents the height of the seedlings.
Therefore, the y intercept tells the mean value of the height of a seedling when no fertiliser is used. Hence, we cay say that the mean value of the height of a seedling when no fertiliser is used is 11 cm.