minta tolong jawab ya!

no.12. 180= ( 3a + 15 ) + (2a - 10 )
= 180 = 3a + 15 + 2a - 10
= 180 = 3a + 2a + 15 - 10
= 180 = 5a + 5
= 180 - 5 = 5a
= 175 = 5a
175/5 = a
= 35 = a
( a + 8 )
= 35 + 8
= 43
no.13. gradiennya = m = -y/x
= -6/9
= -2/3