Tolong beserta caranya

2j = d
j + 56 = 4/5 a = 4/5 ( j+d)
j - 4/5 j = 4/5 d - 56
1/5 j = 4/5 d - 56
1/5 j = 4/5 . 2j - 56
1/5 j = 8/5 j - 56
1/5 j - 8/5 j = -56
-7/5 j = -56
j = 40
jadi d = 2j = 2(40) = 80