A parallelogram has sides 30m and 14m and one of its diagonals is 40m long. Then its area is

let ABCD be the given parallelogram 

area of parallelogram ABCD = 2 x (area of triangle ABC) 

now a = 30m, b = 14m and c = 40m

 s=1/2 x (30+14+40) = 42 

Area of triangle ABC =  $ss-as-bs-c$  

= $4212282$= 168sq m 

area of parallelogram ABCD = 2 x 168 = 336 sq m