SI unit of torque is newton-meter (Nm).

Newton-meter (Nm):

A torque of 1 N m is caused by a force of 1 N acting perpendicular to the moment arm 1 m long.

Mini Exercise

A force of 150 N can loosen a nut when applied at the end of a spanner 10 cm long.

Solution: 

F = 150 N

$L = 10 cm=\frac{10}{100}=0.1m$

Torque Τ = F × L

= 150 \: N\times 0.1m

= 15 Nm

1. What should be the length of the spanner to loosen the same nut with a 60 N force?

Solution:      

F = 60 N

Τ = 15 Nm

L = ?

$L = \frac{T}{F}$

$L = \frac{15}{60}$

= 0.25 m

2. How much force would be sufficient to loosen it with a 6 cm long spanner?

Solution:      

L = 6 cm = $\frac{6}{100}=0.06m$

Τ = 15 Nm

F =?

F= $\frac{T}{L}$

F= $\frac{15}{0.06}=250N$