Boskyville is planting trees along both sides of its streets. the trees will be planted 50 feet apart. the first tree on the block must stand 20 feet from the corner. if the blocks in boskyville are 390 feet long, how many trees will be planted along one block?

The first thing we are going to do for this case is to define the following variable:
 x = number of trees.
 We then have that the equation that represents the problem is given by:
 y = 50 (x-1) + 20
 Rewriting:
 y = 50x - 50 + 20
 y = 50x - 30
 Substituting for y = 390 we have:
 390 = 50x - 30
 We clear x:
 x = (390 + 30) / (50)
 x = 8.4
 nearest whole integer
 x = 8
 
 will be planted along one block about 8 trees.