It costs 30 pesos to enter a currency exchange building. once there, you can exchange 20 pesos for 1 dollar. how many pesos are required to get z dollars? (write your answer as an expression)

Entry fees: 30 pesos; exchange rate: $1 = 20 pesos OR
1 PESO= 1/20 DOLLAR:
This is a linear function of the form y = mx + b,
where b is the entry fee, x the number of $ and y = z = amount of pesos:
z= (1/20).x + 30

The answer is all about the number 4