IF ELSEIF Cost Calculation Structure

Here is the program with some blanks for you to fill in:

 
'Calculate cost of fuel
'depending on grade and gallons
PRINT "How many gallons"
INPUT gallons
PRINT "What grade (R, E, or S)"
INPUT grade$
'
'Calculate cost
'
IF  _________________ THEN

  PRINT "Cost is", 1.2 * gallons, "dollars"

ELSEIF  _________________ THEN

  PRINT "Cost is", 1.3 * gallons, "dollars"

ELSEIF  _________________ THEN

  PRINT "Cost is", 1.4 * gallons, "dollars"

ELSE
  PRINT "You entered an incorrect grade"

END IF

END

Remember that regular costs $1.20, extra costs $1.30, and super costs $1.40.