Go to the number next to the one you cannot subtract from, take one away, and add a one in front of the number you cannot subtract from. e.g.
27 1(1)7 the answer would be 9
-8 -8
for your problem the answer would be 1109
Let $k = the monthly base fee.
The variable cost is $0.30 per minute.
Let
C = total cost in a month
x = minutes used
September:
x = 120 minutes
C = $50
Therefore
k + (0.30)(120) = 50
k + 36 = 50
k = $14
October:
x = 165 minutes
The cost is
C = 14 + (0.3)(165)
C = $63.5
Answer: $63.50
(x/3)+5=2x-70
3[(x/3)+5]=[2x-70]3
x+15=6x-210
+210 +210
x+225=6x
-x -x
5x=225
x=45
