[( c+41+56):2-20]:10=3 /×10
[(c+41+56):2-20]=30
[(c+41+56):2]=30+20
[(c+41+56):2]=50
(c+41+56)=50×2
(c+41+56)=100
c+41=100-56
c+41=44
c=44-41
c=3