Tanya purchased 4 hamners for $11.00 each and 7 scewdrivers for $6.65 each write an expresion for the total cost of the tools. then find the total cost

X=numbers of hammers
y=numbers of  scewdrivers
f(x,y)= total cost in $

f(x,y)=11x+6.65y

f(4,7)=4(11)+6.65(7)=44+46.55=90.55

Sol: an expresion for the total cost of the tools is f(x,y)=11x+6.65 y; 
x=number of hammers
y= number of  scewdrivers.
The total cost is $90.55

Total cost=cost of hammers+cost of screwdrivers

cost of hammers=number of hammers times cost per hammer
cost of screwdrivers=number of screwdrivers tiems cost per screwdriver

number of hammers=4
cost per hammer=11.00
number of screwdrivers=7
cost per screwdriver=6.65
subsiute

cost of hammers=4 times 11.00=44.00
cost of screwdrivers=7 tiems 6.65=46.55

total cost=cost of hammers+cost of screwdrivers
total cost=44.00+46.55=$90.55

total cost=$90.55

What's the denominator