The average (arithmetic mean) of 10, 14, and 3x is 18. What is the value of x? A) 25
B) 26
C) 27
D) 30

Mean=(10+14+3x)/(3)
Which mean value ady stated, 18
18=(10+14+3x)/(3)
54= (10+14+3x)
54-10-14=3x
3x=30
x=10

Hope this can help.

1. 0.3 •4 is the same as 4 groups of 0.32. 7•0.8 is the same as 7 groups of 0.83. it increases by 0.5 every time, so 0.5x4 it increases by 0.9 every time, so 0.9x5. 0.9•12=10.86. 0.47•5=2.35i can finish the next ones in a separate post