Of the two parallel sides of a trapezium, one is 5 cm longer than the other. Find the height of the trapezium if the longer side is 12 cm and its area is 57

Formula is: A=h*(a+b)/2 where a and b are the two parallel sides. 

This gives 57=h*(12+(12-5))/2

h=....

Formula is: A=h*(a+b)/2 where a and b are the two parallel sides.

b=7

a=12

57=h(12+7)/2

h=57*2/19

h=6