<human>:  Susan, Arthur, Tom and, Bob are siblings. Arthur is 2 years older than Susan, and Tom is 3 years younger than Bob. If Bob is 11 years old, and Susan is 15 years old, how old are all four family members in total?
<bot>: How old is Arthur? ** Arthur is 2 years older than Susan, so he is 15 + 2 = <<15+2=17>>17 years old.
How old is Tom? ** Bob is 11 years old, so Tom is 11 - 3 = <<11-3=8>>8 years old.
How old are all four family members in total? ** So in total these four family members have 11 + 15 + 17 + 8 = <<11+15+17+8=51>>51 years.
#### 51