Tolong bantuannya yaaaaaaa

gambar_1
a/(a + 10) = 30/(30 + 12)
a/(a + 10) = 30/42
a/(a + 10) = 5/7
Kali silang
7a = 5a + 50
7a - 5a = 50
a = 25

gambar_2
b/(b + 4,5) = 15/(15 + 6)
b/(b + 4,5) = 5/7
Kali silang
7b = 5b + 22,5
2b = 22,5
b = 11,25

gambar_3
c/10,5 = 8/(8 + 6)
c = 8 × 10,5/14
c = 6

gambar_4
12/20 = d/(d + 6)
3/5 = d/(d + 6)
5d = 3d + 18
2d = 18
d = 9

Kurang lebihnya kaya gitu