def dx(fn, x, delta=0.001):
    return (fn(x+delta) - fn(x))/delta
def solve(fn, value, x=0.5, maxtries=1000, maxerr=0.00001):
    for tries in xrange(maxtries):
        err = fn(x) - value
        if abs(err) < maxerr:
            return x
        slope = dx(fn, x)
        x -= err/slope
    raise ValueError('no solution found')
 
        
             
        
        
        
A good website to learn coding is called Lynda.com. It costs money but its well worth it!
 
        
                    
             
        
        
        
Answer:
#here is code in python.
# read the food bill
tot_bill=float(input("Please enter the food bill:"))
# tax on food
tax=0.06
#choice for tip by user
choice=int(input("enter your choice for tip:(1 for 15%, 2 for 18% and 3 for 20% :)"))
// calculate the total food bill
if choice==1:
    tot_food_bill=tot_bill+tot_bill*tax+tot_bill*(.15)
elif choice==2:
    tot_food_bill=tot_bill+tot_bill*tax+tot_bill*(.18)
elif choice==3:
    tot_food_bill=tot_bill+tot_bill*tax+tot_bill*(.2)
else:
    print("invalid choice:")
#print the total food bill 
print("total food bill is ",tot_food_bill)    
Explanation:
Read the food bill from user and assign it to variable "tot_bill".Initialize the tax=0.06 (i.e. 6%) on the bill.Then ask user to give his choice for tip. if the choice is 1 then tip will be 15%, if 2 then 18% and if choice is 3 Then tip will be 20% of the bill.Calculate the total food bill and assign it to variable "tot_food_bill".
Output:
Please enter the food bill:100                                                                                                                                
enter your choice for tip:(1 for 15%, 2 for 18% and 3 for 20% :)2                                                                                             
total food bill is  124.0