Answer:
[scale]=[drawing]/[real]-----------> [real]=[drawing]/[scale]
scale=3 cm/ 4 m------> 0.75 cm/m
the dimensions of backyard in the drawing are 9 cm x 6 cm
step 1
find the real dimensions of backyard
for 9 cm
[real]=[drawing]/[scale]
[real]=[9]/[0.75]----------> 12 m
for 6 cm
[real]=[drawing]/[scale]
[real]=[6]/[0.75]----------> 8 m
so
the real dimensions of backyard are 8 m x 12 m
[the area of the real backyard ]=8*12--------> 96 m²
the answer is 96 m²