this picture has bad quality, please resend with better picture so i can answer all of them
1. -18 +15x = 3(4x-6) + 3x
-18 + 15x = 12x - 18 + 3x
-18 + 3x = -18 + 3x
3x = 3x
x = All Real Numbers (because we don't know what x is since the equation is 3x = 3x, we can assume that it is all "real" numbers)
2. -10 + 5x = 5(x - 3) + 5
-10 + 5x = 5x - 15 + 5
-10 = -10
Answer Undefined (because the x coefficients canceled out, we don't know what x even is, so we can claim it as undefined.)
Changing the subject of an equation involves solving for another variable in the equation
The equation of t is 
<h3>How to change the subject of the equation</h3>
The equation is given as:
![N=\sqrt[2]{\frac{y_i-y_o}{t^2}}](https://tex.z-dn.net/?f=N%3D%5Csqrt%5B2%5D%7B%5Cfrac%7By_i-y_o%7D%7Bt%5E2%7D%7D)
Rewrite the equation as:

Evaluate the square root of t^2

Multiply both sides by t

Make t the subject, in the above equation

Hence, the equation of t is 
Read more about subject of formula at:
brainly.com/question/657646