20/25 as a decimal is 0.8
1). To multiply with like bases, add the exponents ===> 5² x 5⁵ = 5⁷
2). Same rule. e² x e⁷ = e⁹
3). Same rule, but make sure to start with like bases.
2a⁵ x 6a = (2 x 6) (a⁵ x a¹) = 12 a⁶
4). Same rule, but make sure to start with like bases.
4x² (-5)x⁶ = (4) (-5) (x² x⁶) = -20x⁸
5). To divide with like bases, subtract the denominator (divisor) exponent
from the numerator (dividend) exponent. ===> 7⁹ / 7³ = 7⁶
6). Same rule. v¹⁴ / v⁶ = v⁸
7). Same rule, but make sure to start with like bases.
15w⁷ / 5w² = (15/5) (w⁷/w²) = 3 w⁵
8). Same rule, but make sure to start with like bases.
10 m⁸ / 2m = (10/2) (m⁸ / m¹) = 5m⁷
9). Same rules. Add exponents to multiply, subtract them to divide.
( 2⁵ x 3⁷ x 4³ ) / (2¹ x 3⁵ x 4) = (2⁵ / 2¹) x (3⁷ / 3⁵) x (4³ / 4¹) = 2⁴ x 3² x 4²
10). (4¹⁵) x (-5)⁶ / (4¹² x (-5)⁴ ) = (4¹⁵/4¹²) x [ (-5)⁶/(-5)⁴ ] = 4³ x (-5)² = 4³ x 5²
11). (6⁷ x 7⁶ x 8⁵) / (6⁵ x 7⁵ x 8⁴) = (6⁷ / 6⁵) x (7⁶ / 7⁵) x (8⁵ / 8⁴)
You can finish it from here, you Crazy Unicorn you.
12). [ (-3)⁶ x 10⁵ ] / [ (-3)⁴ x 10³ ] = [ (-3)⁶ / (-3)⁴ ] x (10⁵/10³)
The last step is yours. Take it !
Just 9
I'm not sure for the second one but I think 1 ft
Two lines are perpendicular between each other if their slopes fulfills the following property

where m1 and m2 represents the slopes of line 1 an 2, respectively.
To find the slope of a line we can write it in the form slope-intercept form

Our original line is

Then its slope is

Now we have to find the slope of the second line. Using the first property,

Then the second line has to have a slope of 8.
The options given to us are:

Then we have to determine which of these options have a slope of 8. To do that we write them in the slope-intercept form:

Once we have the options in the right form, we note that the only one of them that has a slope of 8 is the last one.
Then the line perpendicular to the original one is
The straight lines mean absolute value
so x = -16 and x = 16