Question 259504
Let the length of the rectangle be "L" and Width be "B".

From the problem we know that L is 3cm more than B. So if we put it in the form of an equation,

L = B + 3 --> (1)

The formula to calculate the area of a rectangle is.. 
A = L * B 
where A = Area of the rectangle
L = Length of the rectangle
B = Breadth of the rectangle 
Now from the problem we have the following values.. 
A = 70
L = B + 3 -->(From (1) above ) 
Substituting these values in the above formula.. 
70 = (B + 3) * B
70 = B*B + 3*B
70 - 70 = B^2 + 3B - 70 -->(Subtracting 70 from both sides)
0 = B^2 + 3B - 70
0 = B*B + (10B - 7B) - (10 * 7)  --->(Since 10B - 7B = 3B and 10*7 = 70)
0 = B(B + 10) - 7(B + 10)  --> (Taking out the common figures which are "B" and "-7" )

0 = (B + 10)(B - 7) -->(Since (B + 10) is common )

So we have the following conclusions from above,

B + 10 = 0   OR B - 7 =0
B = -10     OR  B = 7

Now since B represents the width of the rectangle it cannot be negative. So the correct answer would be B = 7

So the breadth of the rectangle is 7cm

From (1) above we know that,
L = B + 3

Substituting the value for B..
L = 7 + 3
L = 10

So the length of the rectangle is 10cm