Linear Momentum = Mass x Velocity

Now
Velocity = Displacement/Time
Velocity = L/T
So
Linear Momentum= M x LT^-1

So Dimensional Formula of Linear Momentum= M¹L¹T^-1
SI unit of Linear Momentum is kg ms^-1

Specific Gravity formula is

Specific Gravity = Density of Body/Density of Body at 4^oC

Now
Density = Mass/Volume
Density = M/L³

So Dimensional Formula of Specific Gravity= M⁰L⁰T⁰
Note: Specific Gravity is defined as change in Density of Body over Density of Body at 4^oC. Now we know that both Density of Body and Density of Body at 4^oC has same dimensions i.e. Mass/Volume so same units cancel each other leaving numeric value only. So Specific Gravity has no unit.

Density is defined as the mass per unit volume. So its formula is

Density = Mass/Volume

Dimensional Formula of Mass = M¹L⁰T⁰
Dimensional Formula of Volume = M⁰L³T⁰

Putting these values in above equation we get,
Dimensional Formula of Density =M¹L^-3T⁰
SI unit of Density is kg/ m³

We know
Volume = Length x Breadth x Height
Volume = L x L x L
Volume = L³

So Dimensional Formula of Volume = [M⁰ L³ T⁰]
SI unit of Volume is m³

To calculate Dimensional Formula of Area, we need to know its formula

Area = Length x Breadth
Area = L x L
Area = L²

So Dimensional Formula = [M⁰ L² T⁰]
SI unit of Area is m²