Tolong dijawab Ya besok saya ulangan

36.a
37.b/c
kalo salah maaf ya

1/f=1/si+/1so
1/15=1/si+1/20
1/si=1/15-1/20
1/si=4/60-3/60
1/si=1/60
si=60

M=si/so
=60/20
=3

semoga membantu☺