Whats the answer can someone answer please

Step-by-step explanation:

21.

4(x + 7) - 2x

4x + 28 - 2x

2x + 28

2x + 28

22.

8(a + b) + 5(2a - 5b)

8a + 8b + 10a - 25b

18a - 17b

18a - 17b

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

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

dc=6 square root of 3 and ac is 12 square root 3

c and d

step-by-step explanation:

square root of 3/2 = 18/c

cross multiply to get 18*2=√3*c

36/√3 * √3/√3 = c

c= 36*√3/3

c=12√3