Alternatively calculation php str_replace

Formula = $ " ((total mass / 1000) + production costs + selling expenses + administrative expenses + profit amount) * * cost coefficient area coefficient "  // formula
 // number 
$ Total = 10 ; // total 
$ production_cost = 1 ; // production costs 
$ sales_cost = 2 ; // cost of sales 
$ management_cost = 3 ; // administrative expenses 
$ profit = 4 ; // profit amount 
$ costfactor = 5 ; // cost coefficient 
$ replace = array ($ total, $ production_cost, sales_cost $, $ management_cost, Profit $, $ costfactor, ' . 1 '); 
$ Formula = str_replace ($ Find, Replace $, $ Formula);   // replace string 
print_r ($ Formula); Die;
 // Price 
$ = unitPrice, the eval ( " return $ Formula " ); // string PHP code is calculated as