In a garden, a birdbath 2 ft 6 in. tall casts an 18 in. shadow at the same time an oak tree casts a 90 foot shadow. How tall is the oak tree in feet?

150 ft tall

Step-by-step explanation:

first, lets first convert 2ft 6in to ft:

since ft=12 in, 6=0.5 ft

thus, the height of the birdbath is 2+0.5 ft=2.5ft

now, lets convert 18 inch shadow to ft:

since ft=12 in, 18=1.5 ft

now, we can use the following proportions to solve this problem:

2.5/1.5=x/90

1.5x=90*2.5

1.5x=225

x=225/1.5

x=150

Thus, the oak tree in the garden is 150 ft tall