Lookup number in column and interpolate result

If i have two columns
A1=10, B1=100
A2=20,B2=200

In cell D1 is the number 7
In cell E1 i need to lookup and find cell D1(7) in column A:A and return the interpalated value from Column B:B

find that D1 is inbetween 10 and 20 and work out the correct value between 100 and 200. answer should be 150

Im using whole numbers in this example but in reality i need to use numbers to 3dp, so the rounding up and down etc i tried did not work.
I'm using numbers more like
15.253, 25555.365
19.657, 56325.268
and i want to find what the equivalent of 18.0 is between these numbers?
Thanks for any help given.

Hi,

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Cheers,