Amath teacher drove past a farmyard full of chickens and pigs. the teacher noticed that there were a total of 30 heads and 100 legs. how many pigs were ther

We know each animal has one head.  But a chicken has 2 legs and a pig has 4 legs.  Set up a system of equations.

2x+4y=100 (where x is the number of chickens and y is the number of pigs)
x+y=30

You can do the solving work (because is looks really messy in paragraph form) but if you solve for x in the bottom equation you get -y+30.  Now plug in (-y+30) in for x in your top equation and solve for y to get 20.  Since you know that x = -y+30, plug in 20.  x=-20+30 simplifies to x=10.

x (number of chickens) = 10
y (number of pigs) = 20

I hope this helps your solving systems of equations.

J= r + 9 because since jessica rode 9 more miles than roger, you add 9 miles to rogers mileage.