Answer
$a-\phi(15)=8\\
b-\phi(2)=1\\
c-\phi(5)=4\\
d-\phi(12)=4\\
e-\phi(11)=10\\
f-\phi(1)=1\\$
Work Step by Step
$\phi(n) \,\,\,is\,defined\,as\,follows:\\
For\,each\,integer\,\,\,\,
n \geq 1, \\\phi(n)\,is\,the\,number\,of\,positive\,integers\,less\,than\,or\,equal\,\,
to\,n\,\,\\that\,have\,no\,common\,factors\,with\,\,n\,\,except\,\,\pm 1. \\
a-\phi(15)=8\\
because\,\,there\,are\,eight\,positive\,integers\,less\,than\,\,\\
or\,\,equal\,to\,15\,that\,have\,no\,common\,factors\,with\,15\,\,except\pm 1;\\
namely,1,2,4,7,8,11,13\,and\,14 \\
b-\phi(2)=1\\
because\,\,there\,are\,one\,positive\,integers\,less\,than\,\,\\
or\,\,equal\,to\,2\,that\,have\,no\,common\,factors\,with\,2\,\,except\pm 1;\\
namely,1\\
c-\phi(5)=4\\
because\,\,there\,are\,four\,positive\,integers\,less\,than\,\,\\
or\,\,equal\,to\,5\,that\,have\,no\,common\,factors\,with\,5\,\,except\pm 1;\\
namely,1,2,3,4\\
d-\phi(12)=4\\
because\,\,there\,are\,four\,positive\,integers\,less\,than\,\,\\
or\,\,equal\,to\,12\,that\,have\,no\,common\,factors\,with\,12\,\,except\pm 1;\\
namely,1,5,7,11\\
e-\phi(11)=10\\
because\,\,there\,are\,one\,ten\,integers\,less\,than\,\,\\
or\,\,equal\,to\,11\,that\,have\,no\,common\,factors\,with\,11\,\,except\pm 1;\\
namely,1,2,3,4,5,6,7,8,9,10\\
f-\phi(1)=1\\
because\,\,there\,are\,one\,positive\,integers\,less\,than\,\,\\
or\,\,equal\,to\,1\,that\,have\,no\,common\,factors\,with\,1\,\,except\pm 1;\\
namely,1\\
$