Ohm's law equation used to solve this problem is;
V = IR
where V - voltage
I - current passing
R - resistance
voltage is the potential difference between 2 points and current passing through these 2 points is proportional to the potential difference, in other words voltage.
V∞I
Resistance is the constant in the equation
the current required to pass through is 0.05 A (amperes)
the battery voltage is 3.0 V (volts)
substituting these values
3 V = 0.05 A * R
R = 3/0.05
R = 60 Ω (ohms)