Question 1182453
The general formula for voltage current and number of turns in a transformer is


{{{ Np/Ns = Vp/Vs = Is/Ip}}}

where N is number of turns is the voltage
I is the current

p is primary coil
s secondary  coil

{{{Vp/140 = 3.5/10}}}

Vp = 14 *3.5 =49 Volts