Answer:

Step-by-step explanation:
Given voltage of primary coil is 
And voltage of secondary coil is 
A transformer is a device that contains primary and secondary coil. These coils are mounted on soft iron. The change in voltage depends upon the number of turns of primary coil
and secondary coil
.
Following equation represents the relation between them.

Then, ratio of the number of wire turns on the primary coil to the number of turns on the secondary coil is

Answer:
12.5
Step-by-step explanation:
Step 1:
0.4 ( 3b + 10 ) = 19 Equation
Step 2:
1.2b + 4 = 19 Multiply
Step 3:
1.2b = 15 Subtract 4 on both sides
Step 4:
15 ÷ 1.2 Divide
Answer:
b = 12.5
Hope This Helps :)