What is meant by the "subject" of a formula?

In the formula v=u+at, make 'u' the subject.

In the formula l=a+(n−1)d, make 'd' the subject.

Given the formula A=πr2 for the area of a circle, make 'r' the subject.

In the formula for the simple pendulum, t=2πgl​​, make 'l' the subject.

Using the same formula, t=2πgl​​, make 'g' the subject.

In the formula v2−u2=2as, make 'u' the subject.

Given the formula A=π(R2−r2), make 'R' the subject.

In the formula v=wa2−x2​, make 'a' the subject.

Given v2=u2+2as, find the value of 'a' when v=10, u=0, and s=10.

Given s=ut+21​at2, find the value of 't' when u=0, a=5, and s=250.

Given t=2πgl​​, find the value of 't' when l=490, g=10, and π=722​.

The formula for the volume of a cone is v=31​πr2h. Find the value of 'r' when v=132, h=14, and π=722​.

According to Pythagoras' theorem, x=a2+b2​. Find the value of 'b' when x=25 cm and a=24 cm.

The energy of a moving object is given by E=mgh+21​mv2. Make 'v' the subject of the formula.