**Bending Stress**

To determine the bending stress in the rolled steel joist (RSJ), we need to calculate the moment of inertia (I) of the section and the bending moment (M) at the given point.

The moment of inertia (I) can be calculated using the formula:

I = (b * h^3) / 12

Where:
- b is the width of the section (flange width)
- h is the height of the section (web height)

In this case, the width of the section (b) is the sum of the top and bottom flange widths, so b = 2 * 150 mm = 300 mm.
The height of the section (h) is the sum of the web height and the flange thickness, so h = 300 mm + 2 * 25 mm = 350 mm.

Plugging these values into the formula, we get:

I = (300 mm * 350 mm^3) / 12 = 3,937,500 mm^4

The bending moment (M) at the given point can be calculated using the formula:

M = (w * L^2) / 8

Where:
- w is the uniformly distributed load
- L is the span length

In this case, the uniformly distributed load (w) is 80 kN/m, and the span length (L) is 4 m.
Plugging these values into the formula, we get:

M = (80 kN/m * 4 m^2) / 8 = 160 kNm

Now, we can calculate the bending stress (σ) using the formula:

σ = (M * y) / I

Where:
- σ is the bending stress
- y is the distance from the neutral axis to the point of interest

For the given point at 1/4 span, the distance from the neutral axis to the point of interest can be determined by:

y = h / 2

Plugging the values into the formula, we get:

y = 350 mm / 2 = 175 mm

Now we can calculate the bending stress at 1/4 span:

σ = (160 kNm * 175 mm) / 3,937,500 mm^4 = 7.12 MPa

**Shearing Stress**

To determine the shearing stress in the RSJ, we need to calculate the shear force (V) at the given point.

The shear force (V) can be calculated using the formula:

V = (w * L) / 2

Where:
- w is the uniformly distributed load
- L is the span length

In this case, the uniformly distributed load (w) is 80 kN/m, and the span length (L) is 4 m.
Plugging these values into the formula, we get:

V = (80 kN/m * 4 m) / 2 = 160 kN

Now we can calculate the shearing stress (τ) using the formula:

τ = (V * A) / (I * h)

Where:
- τ is the shearing stress
- A is the area of the section (flange area + web area)

The area of the section can be calculated as:

A = (2 * b * t) + (h * t)

Where:
- t is the thickness of the section (fl