This product involves zero. So, you don't have to bother and compute all the factor, because if you multiply anything by zero you get zero.
We can't tell. Contrary to what you led us to believe, there is no triangle illustrated, and we need one for the new one to be similar to.
Answer:

Step-by-step explanation:
S = (x1,y1) = (0,-5)
T = (x2,y2) = (-8,-7)
<u>Using distance formula to find the length of ST</u>.
![|ST|= \sqrt{(x_2-x_1)^2+(y_2-y_1)^2} \\\\|ST| = \sqrt{(-8-0)^2+(-7-(-5))^2} \\\\|ST| = \sqrt{(-8)^2+(-7+5)^2} \\\\|ST| = \sqrt{64+(2)^2}\\\\|ST| = \sqrt{64+4} \\\\|ST| = \sqrt{68} \\\\|ST| = 8.2 \ units\\\\\rule[225]{225}{2}](https://tex.z-dn.net/?f=%7CST%7C%3D%20%5Csqrt%7B%28x_2-x_1%29%5E2%2B%28y_2-y_1%29%5E2%7D%20%5C%5C%5C%5C%7CST%7C%20%3D%20%5Csqrt%7B%28-8-0%29%5E2%2B%28-7-%28-5%29%29%5E2%7D%20%5C%5C%5C%5C%7CST%7C%20%3D%20%5Csqrt%7B%28-8%29%5E2%2B%28-7%2B5%29%5E2%7D%20%5C%5C%5C%5C%7CST%7C%20%3D%20%5Csqrt%7B64%2B%282%29%5E2%7D%5C%5C%5C%5C%7CST%7C%20%3D%20%5Csqrt%7B64%2B4%7D%20%5C%5C%5C%5C%7CST%7C%20%3D%20%5Csqrt%7B68%7D%20%5C%5C%5C%5C%7CST%7C%20%3D%208.2%20%5C%20units%5C%5C%5C%5C%5Crule%5B225%5D%7B225%7D%7B2%7D)