Find the equation of the straight line if it pass though the origin and has a gradient of 3?

The equation of a straight line passing through the origin with a gradient of 3 can be written in the form y = mx, where m is the gradient.

Therefore, the equation of the straight line is y = 3x.

Equation of a straight line passing through the origin:

```
y = mx
```

where:

- y is the dependent variable (the value you're solving for)
- x is the independent variable
- m is the slope or gradient of the line

Given information:

- The line passes through the origin, so the y-intercept is 0.
- The gradient of the line is 3.

Substituting the given values into the equation:

```
y = 3x
```

Therefore, the equation of the straight line is y = 3x.