Answer:
![w=8cm\\h=18.75cm](https://img.qammunity.org/2021/formulas/mathematics/high-school/2opxeast5k3xo9sj4dxl9aop7pn3sk471h.png)
Explanation:
Let:
![w=Width\\h=Initial\hspace{3}height\\h_m=Modified\hspace{3}height\\\\Where:\\\\h_m=h-3](https://img.qammunity.org/2021/formulas/mathematics/high-school/oh54olr3eoqje24w19fwr1rs14p0qb4iox.png)
The area of the cardboard can be calculated using the formula to find the area of a rectangle:
![A=w*h](https://img.qammunity.org/2021/formulas/mathematics/college/p04h2vtdz130ih59nxvaw2v57gqor8ie9w.png)
The area of the new cardboard would be:
![A=w*h_m\\\\Where:\\\\w=8\\h_m=h-3\\A=126](https://img.qammunity.org/2021/formulas/mathematics/high-school/ef58cnpvpmfoo1e6kfuy7mwk33h3u7arhm.png)
So:
![126=8*(h-3)\\\\126=8h-24](https://img.qammunity.org/2021/formulas/mathematics/high-school/9ligjay0esh5p7uaytm63c6f51vv370y50.png)
Solving for h:
![126+24=8h\\\\150=8h\\\\h=(150)/(8) =(75)/(4) =18.75cm](https://img.qammunity.org/2021/formulas/mathematics/high-school/ufy77abdw1gnv1plecxczmk1j4rhzwoc3l.png)
Therefore, the dimensions of the initial cardboard are:
![w=8cm\\h=18.75cm](https://img.qammunity.org/2021/formulas/mathematics/high-school/2opxeast5k3xo9sj4dxl9aop7pn3sk471h.png)
Translation:
Sea:
![w=Ancho\\h=Altura\hspace{3}inicial\\h_m=Altura\hspace{3}modificada\\\\Donde:\\\\h_m=h-3](https://img.qammunity.org/2021/formulas/mathematics/high-school/dmivvax4c422mmkd03x90bck7v92z33nhn.png)
El área de la cartulina se puede calcular usando la fórmula para encontrar el área de un rectángulo:
![A=w*h](https://img.qammunity.org/2021/formulas/mathematics/college/p04h2vtdz130ih59nxvaw2v57gqor8ie9w.png)
El área de la nueva cartulina sería:
![A=w*h_m\\\\Donde:\\\\w=8\\h_m=h-3\\A=126](https://img.qammunity.org/2021/formulas/mathematics/high-school/48eiy0rzw3to1sdvroi1aooeo4a30fo8dk.png)
Entonces:
![126=8*(h-3)\\\\126=8h-24](https://img.qammunity.org/2021/formulas/mathematics/high-school/9ligjay0esh5p7uaytm63c6f51vv370y50.png)
Resolviendo para h:
![126+24=8h\\\\150=8h\\\\h=(150)/(8) =(75)/(4) =18.75cm](https://img.qammunity.org/2021/formulas/mathematics/high-school/ufy77abdw1gnv1plecxczmk1j4rhzwoc3l.png)
Por lo tanto, las dimensiones de la cartulina inicial son:
![w=8cm\\h=18.75cm](https://img.qammunity.org/2021/formulas/mathematics/high-school/2opxeast5k3xo9sj4dxl9aop7pn3sk471h.png)