Formula :

Plug in the values :

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Answer:550----------------------------------
You can't see the picture, please reach out once i can see it
I=PRT
Interest=I
P=principal
R=rate in decimal
T=time in years
given
asuming 640 is the principal and not the interest
P=640
R=3%=0.03
T=2
I=640*0.03*2
I=19.2*2
I=38.4
interst=$38.40
The amount of board is 5.5 feet because 18*5.5=99 and 144-45 is 99.