-- First, we have to decide how to handle the two resistors.
The effective resistance of resistors in series is the sum
of their individual resistances. That is, they act like a single
resistor, whose resistance is the sum of all of them.
So in this question, the 4.0 ohms and the 7.5 ohms act like a
single resistor of 11.5 ohms.
-- The current in the circuit is
(the supply voltage) / (the total resistance)
= (9.0 volts) / (11.5 ohms)
= 0.783... Ampere (rounded)
The vertical component of the initial velocity is 
The horizontal component of the initial velocity is 
The horizontal displacement when the object reaches maximum height is 
The given parameters;
the horizontal displacement of the object, = x
the vertical displacement of the object, = y
acceleration due to gravity, = g
time of motion, = t
The vertical component of the initial velocity is given as;

The horizontal component of the initial velocity is calculated as;

The time to reach to the maximum height is calculated as;

The horizontal displacement when the object reaches maximum height is calculated as;

Learn more here: brainly.com/question/20689870
Frequency = 1/time period = 1/0.05 = 20s^-1.