`a)`
\(\%m_{^{65}Cu}=100-73=27\%\)
`->M_{Cu}={63.73+65.27}/{100}=63,54(g//mol)`
`n_{Cu_2O}={7,154}/{63,54.2+16}=0,05(mol)`
`->n_{Cu}=0,1(mol)`
\(\to m_{^{63}Cu}=0,1.63,54.73\%=4,63842(g)\)
`b)`
`\%m_{Cu}={63,54}/{63,54+32+16.4}.100\%\approx 39,827\%`