I dunno how to solve this

9

Step-by-step explanation:

First off you need to find the interval that four falls in.  

Four is not less than three so you can rule out the first one, four is not greater than 10 so you can rule out the last one.  But four is greater than three and less than ten, so it falls in the second interval.

So, now you can substitute four in for x for the second equation

4^2-7

16-7

=9

second option

step-by-step explanation:

the measures of a triangle equal 180. use that to find x.

2x+3x+4x=180

9x=180

9x/9=180/9

x=20

now you know x, you know angle a is 40°, angle b is 60°, angle c is 80°.

because angle a is 40°, the first option doesn't work.

because angle b is 60°, the second option does work.

when you add angle a and b, you get 100°. complementary means it equals 90°, so the third option doesn't work.

when you add angle a and c, you get 120°, which is not 100.