Question

tell me that one in notebook with proper solution

Answer 1

This may be right one

Answer 2

area of first face=15 sq m
l×h=15.........(1)

area of second face=20 sq m
b×h=20......(2)

area of third face=12sq m
l×b=12.........(3)

From 1 we find that
$l = \frac{15}{h} \\ putting \: this \: in \: (3)\: we \: get \\ \frac{15}{h} \times b = 12 \\ b = \frac{12h}{15} = \frac{4h}{5} .....(4) \\ solving \: (2) \: and \: (4) \: for \: b \: and \: h \\b \times h = 20 \\ \frac{4h}{5} \times h = 20 \\ {h}^{2} = \frac{20 \times 5}{4} \\ {h}^{2} = 25 \\ h = 5m\\ \\ \: l = \frac{15}{5} = 3m \\ b = \frac{4 \times 5}{5} \\ b = 4m \\ now \: v = lbh \\ v = 3 \times 4 \times 5 = 60 {m}^{3}$