// ĠReturn Ġthe Ġsum Ġof Ġprices Ġfor Ġall Ġthe Ġproducts Ġordered Ġby Ġa Ġgiven Ġcustomer Ċ fun Ġmoney Sp ent By ( customer : ĠCustomer ): ĠDouble Ġ= ĊĠĠĠ Ġcustomer . orders . flatMap ( Order :: products ). sum By Double ( Product :: price ) Ċ