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

b. 24 mm

step-by-step explanation:

use the pythagorean theorem.

a^2 + b^2 = c^2

a^2 + 7^2 = 25^2

a^2 + 49 = 625

a^2 = 576

a = 24

answer: b. 24 mm

x = ±sqrt(10)

step-by-step explanation:

5 - 2x² = -15

subtract 5 from each side

5-5 - 2x² = -15-5

-2x^2   = -20

divide by -2 on each side

-2x^2   /-2= -20/-2

x^2 =10

take the square root on each side

sqrt(x^2 )=±sqrt(10)

x = ±sqrt(10)

check:

5 - 2x² = -15

+sqrt(10)

5 - 2(sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15

-sqrt(10)

5 - 2(-sqrt(10))² = -15

5 -2(10) = -15

5 -20 = -15

-15 = -15