Let's apply the mirror equation which is:

`1/d_o + 1/d_i=1/f`

where `d_o` ` `- object distance, `d_i` ` `- image distance and `f ` - focal length.

Note that, magnification factor is the ratio of image distance to object distance.

Magnification factor `= ` `-d_i/d_o`

Since magnification factor is...

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Let's apply the mirror equation which is:

`1/d_o + 1/d_i=1/f`

where `d_o` ` `- object distance, `d_i` ` `- image distance and `f ` - focal length.

Note that, magnification factor is the ratio of image distance to object distance.

Magnification factor `= ` `-d_i/d_o`

Since magnification factor is +3 and object distance is 30 cm, then

`3=-d_i/30`

` `

Isolate `d_i` .

`-90=d_i`

` `

Then, substitute `d_o=30` cm and `d_i=-90` cm to the mirror equation.

`1/30 + 1/(-90)=1/f`

` `

To simplify the equation, multiply both sides by the LCD which is 90f.

`90f*(1/30 + 1/(-90))=(1/f) *90f`

`3f-f=90`

`2f=90`

Solve for f.

`f=90/2`

`f=45` cm

Moreover in curved mirrors, the focal length is half the raduis of the curvature of mirror. So,

`f = R/2`

Substitute value of f.

`45=R/2`

Isolate R.

`45*2 = R`

`90=R`

**Hence, the raduis of curvature of the mirror is 90 cm.**