$\backslash$table$[[,\backslash$table$[[$Long$-$Run Total Cost $($Dollars$)],[$Quantity$]]],[$Firm $1,$Firm $2,$Firm $3,$Firm $4,],[1,180,120,150,210],[2,350,250,300,340],[3,510,390,450,490],[4,660,540,600,660],[5,800,700,750,850],[6,930,870,900,1,060],[7,1,050,1,050,1,050,1,290]]$

Refer to Table $14-12.$ Which firm has constant returns to scale over the entire range of output?

a$.$ Firm $3$

b$.$ Firm $4$

c$.$ Firm $1$

d$.$ Firm $2$