Question 663303
This is a very common type of problem.
Let A be the number of apples and O be the number of oranges.
You are told
{{{4A + 2O = 100}}} we are using cents here instead of dollars
{{{2A + 3O = 70}}} 
You have two equations and two unknowns. So you can solve this one
Now you can use your favorite method to solve.
Let's use substitution
{{{4A + 2O = 100}}}
{{{2A + O = 50}}}
{{{O = 50 - 2A}}}

Now use that and plug it into the second equation as follows
{{{2A + 3O = 70}}}
{{{2A + 3*(50-2A) = 70}}}
{{{2A + 150 - 6A = 70}}}
{{{-4A = -80}}}
{{{A = 20}}} so an apple is 20 cents
If an apple it 20 then plug in to find the cost of an orange
{{{4*20 + 2O = 100}}}
{{{80 + 2O = 100}}}
{{{2O = 20}}}
{{{O = 10}}} oranges are a dime. Go not sure what store you shop at, but fruit is a steal :)

Check you answer using the second equation. Does
{{{2A + 3O = 70}}}???