The athletic department bought a total of 29 basketballs and footballs at a cost of $1000. If basketballs cost $30 each and footballs cost $40 each, how many footballs were bought?

Answer 1

You are dealing with two equations in 2 unknowns : )
b + f = 29 is equation 1)
30b + 40f = 1000 is equation 2)
You could re-arrange equation one for a variable and sub it into equation 2... or use the method of "elimination" to solve : )