hallo semua tolong d bantu yaa

u7 = -5
u11 = -13

a+6b = -5
a+10b = -13 (dikurangi)
-4b= 8
b = 8/-4
b = -4

masukkan b = -4 masukkan ke a+6b = -5
a + 6(-4) = -5
a -24 = -5
a = -5 +24
a = 19

u15 = 19+ (14)-4
= 19 -56
= -37

s15 = 1/2.15 (19-37)
= 1/2 . 15. -18
= -135

cmiiw