Applying multiple row formulas to one cell

Greetings,

I have a list of bills with increases and some with percentage increases I am trying to write the proper formula for. I believe it would be a nested IF function.

For example, A1 = title, B1 would be current amount, C1 would be dollar increase, D1 would be percentage increase, E1 would be the increase amount, and F1 would be the total of E1 + B1.

How would I write the formula for E1 to calculate based off cells C1 or D1 either having an amount of be blank? So far I have figured out IF(C1="",0,C1+B1) but can't figure out how to also have D1 also apply same rules, except multiplying a percentage.

I know I could do this a more manual way, but I have a college degree that used a bit of Excel and am always trying to use it to keep skills sharp and learn things I can't figure out, on my own.

Appreciate any input!