Can someone explain substitution more clearly?

As in solving systems by substitution. I'm genuinely stumped, can the process be explained in a coherent and straightforward manner with examples?

Approximately how many kilometers are covered in a 9 mile race?

Tom viaja 60 millas por hora yendo a una ciudad vecina y 50 millas por hora regresando usando la misma carretera. condujo un total de 5 horas ida y vuelta cual es la distancia desde la casa de Tom hasta la ciudad que visitó?

F (x) = x^3-x^2-21x+45; x+5

14. (-7ab) (-6c) (-2) =

Jake owes $3,400 on his credit card. he is not charging any additional purchases because he wants to get this debt paid in full. the card has an apr of 13.9 percent.

What is 2 (9) 0-7+3 to the 3rd power

Mr. Johnson is buying paint to paint the garage wall. He needs to know the area of the wall in order to know how much paint he will need to buy. The wall is 22 feet wide and 11 feet tall. What is the area of the garage wall? A. 242 square ft B.

What percent of 2150 is 688

The half-life of Sodium-24 is 15 hours. If you start with 600 grams of sodium-24 how much would be left after 4 days? Which of the following equations could you use to solve for the amount of grams left after 4 days?

Julia can finish a 20-mile bike ride in 1.2 hours. Katie can finish the same bike ride in 1.6 hours. To the nearest tenth of a mile, how much faster does Julia ride than Katie?