H=150cm
Because these rectangles are similar then they can be dilated to get to the same size as the other.
First you want to find what the scale factor (dilation degree) from the big rectangle to the small. So to do this you want to but your SMALLER value on the top while the BIGGER value on the bottom of your fraction to find the scale factor. This would then look like 60/84. You could simplify this fraction to 5/7.
You can then use this fraction to multiply by the other side of the big rectangle so that you find h. 210*5/7=1050/7. When this is simplified you will get 1050/7=150