Wo liegt mein Syntaxfehler?

[Lukas.]

Hallo,

so gehts prima:

echo('[
{"date":"1 \/ 2014","Summe":'.$arr_Min2[0].'},
{"date":"2 \/ 2014","Summe":4500},
{"date":"3 \/ 2014","Summe":5100},
{"date":"4 \/ 2014","Summe":3699}
]');

So aber nicht:

echo('[
{"date":"1 \/ 2014","Summe":'.$arr_Min2[0] + $arr_Min2[1] + $arr_Min2[2].'},
{"date":"2 \/ 2014","Summe":4500},
{"date":"3 \/ 2014","Summe":5100},
{"date":"4 \/ 2014","Summe":3699}
]');

Wie kann ich innerhalb des Strings meine Rechenoperation durchführen?

Lukas