Question 673929
Just plug in the numbers in place of the letters. 
If a=10 and b=2, look at ab and know that it'll be 10x2, since whenever two numbers/variables are next to each other they'll be multiplied. 
Therefore a/b will equal 10/2, since the / means division always. 
Put it together!
10x2 - 10/2
10x2=20
10/2=5
20-5=15
~*15*~