l = b + 6cm

2l + 2b = 60cm

2 (b + 6cm) + 2b = 60cm

2b + 12cm + 2b = 60cm

4b + 12cm = 60cm

4b = 60 – 12

4b = 48cm

b = 48/4 = 12cm

l = 12 + 6 = 18cm

Area = l x b = 12cm x 18cm = 216 cm²

Verified answer

[tex]\large \colorbox{red}{\orange{Answer-}}[/tex]

l=b+6

2l+2b=60

2(b+6) + 2b = 60

2b+ 12 + 2b =60

4b +12 =60

4b=60–12

4b=48

b=48/4 =12

l=12+6 =18

area =l x b = 12 x 18 =216

A bit of a long winded way but shows the method to those not so comfortable with formulas etc