You and friend purchase an equal number of magazines. your magazine costs 1.50 eachand your friends costs 2.00 each total cost for both is 10.50. solve equation

So we will use n= total number of magazines each 

we start with $2n and $1.50n

then we add $2 and $1.50 =  $3.50n

with that we put $3.50 into an equation  $3.50n = $10.50

so now lets get rid of those decimals by taking 3.5 and doubling it to become 7  after that we need to double 10.5 to 21 

so our new equation is 7n = 21

lets get n be itself by dividing 7 from both sides so that on the side with 7n the 7 cancels out

Finally n=21/7  which equals 3 

so they both both 3 magazines each so if your looking for the total number of magazines between then they got 6 magazines

The answer to your question is the last one