6......................................... i mean this is probably wrong but yeah
He can make 12 or 9 because 9x4=36 and 12x3=36
7(3a + 12) = 168 ← ( divide both sides by 7 )
3a + 12 = 24 ← ( subtract 12 from both sides )
3a = 12 ← ( divide both sides by 3 )
a = 4
OR
distribute the parenthesis by 7
21a + 84 = 168 ← ( subtract 84 from both sides )
21a = 84 ← ( divide both sides by 21 )
a = 4
If your looking at a number to a power (in this case, 3 [cubed]), you multiply the base by the exponent. I would start with the 10 - 10x10x10 = 1,000
Next, multiply your answer by 8.3. You now have 8,300 :)