Question

H=K+log(a/c) isolate a

Answer 1

H=k+log(a/c)
H-k = log(a/c)
e^{h-k}=a/c
a = ce^{h-k}

Answer 2

Remember some properties
is no base is stated, assume base 10
and
$log_a(b)=c$ means $a^c=b$
and
$a^{log_a(b)}=b$
and
$log_a(b/c)=log_a(b)-log_a(c)$
and
$x^{a+b}=(x^a)(x^b)$
so

$H=K+log(a/c)$
$H=K+log_{10}(a/c)$
$H=K+log_{10}(a)-log_{10}(c)$
minus K-log10(c) from both sides
$H-K+log_{10}(c)=log_{10}(a)$
convert
$10^{H-K+log_{10}(c)}=a$
$(10^{H-K}(10^{log_{10}(c)}=a$
$(10^{H-K})(c)=a$
$a=c10^{H-K}$