Answer:
Explanation:
21.
4(x + 7) - 2x
4x + 28 - 2x
2x + 28
answer: 2x + 28
22.
8(a + b) + 5(2a - 5b)
8a + 8b + 10a - 25b
18a - 17b
answer: 18a - 17b
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Jhon's solution is wrong
1. first mistake
when you see this
10^5/10^4
the right solution is 10^(5 - 4) = 10^1 or just 10
2. second mistake
6.4/7.2 he inverted the fraction which is wrong
you can only invert the fraction when the power is negative
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now the correct answer is 6.4/7.2 x 10^5/10^4 = 0.88888888888888888888888888888889 x 10
or 0.9 x 10^1
or 8.9