Given this trace data snippet for a request through three microservices, what is the total time spent processing the request?

Given this trace data snippet for a request through three microservices, what is the total time spent processing the request?

{
  "traceId": "abc123",
  "spans": [
    {"service": "A", "duration_ms": 50},
    {"service": "B", "duration_ms": 30},
    {"service": "C", "duration_ms": 20}
  ]
}