formula for Cumulative Percentage (%) ?

hy to all experts,

Here I want a formula in two cells i.e. I8 & I9.
The baseline & Mitigation data is my cumulative Plan for the project.
here I want a formula in the cell I8 & I9 that if I put 28 February so the Plan Percentage should reflect in the cells.

for any reference please check the attached example sheet...

thanks.... in advance