percent abundance for cu-63 can be shown as:
63 x + 65 (1-x) = 62.9296
65 - 62.9296 = 2 x
x = 1.035
thus, percent abundance for cu-63 is 1.035
percent abundance for cu-65 can be shown as:
63 x + 65 (1-x) = 64.9278
65 - 64.9278 = 2 x
x = 0.0361
thus, percent abundance for cu-63 is 0.0361
the mass spectrum of cu-63 showing the intense peak as, this isotope is found in nature more abundantly around 92.38 % in comparison to cu-65 which is found 62.58 % naturally