If the pth term of an arithmetic progression is q and qth term is p, find p+q term. Help

Please help help help!

We know that the pth term will be the first number + (number you want -1) common difference
call first number a and the difference d

so a + (p-1)d
pth term = a+dp -d
we know that q = a+dp-d

consequently the qth term is p so
a+(q-1)d
a+dq-d
So p = a+dq - d

Adding together we see that

p+q = 2a + dp + dq or p+q = 2a+d(p+q)
which means one term is posite one is negative