tolong bantuannya yaa guyss:)

jawab

a tegak lurus b
a.b = 0
-2(2m) + 3(7) -1(1) = 0
-4m +21- 1 = 0
-4m + 20 = 0
m  = 5

a tegak lurus c
ac = 0
-2(3m) + 3(n) - 1(-3)= 0
-6m - 3n + 3 = 0
-6(5) - 3n + 3 = 0
-30  - 3n + 3 = 0
- 27 - 3n = 0
3n = 27
n = 9 


m + n =  5 + 9 
m + n = 14