Given the Arithmetic sequence -LSB- math -RSB- a_1 , a_2 , a_3 , a_4 39 , 45 , 51 , 57 , \ dots -LSB- / math -RSB- What is the value of -LSB- math -RSB- a _ -LCB- 42 -RCB- ? -LSB- / math -RSB-
Given the Arithmetic sequence -LSB- math -RSB- a_1 , a_2 , a_3 , a_4 , 45,51,57,63 , \ dots -LSB- / math -RSB- , What is the value of -LSB- math -RSB- a _ -LCB- 34 -RCB- ? -LSB- / math -RSB-