Answer: r=5%
Explanation:
I=Prt
I/P=Prt/P
I/P=rt
I/(P*t)=rt/t
r=I/Pt
r=63/(420*3)
r=21*3/(420*3)
r=21/420
r=1/20
r=0.05
r=0.05 * 100%
r=5%
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