Well - what are the two most prominent figures here? You'll have to round up in this case to the nearest whole number in the second figure.
So - you have 136 million 500 thousand. That rounds up to 140 million using the two most significant figures no? (the 1 and the 4) You then have 140,000,000 which in scientific notation, or standard form, gives you 1.4 x 10 to the power of the number decimal places need to get 1.4 back to 140 million. Which is eight decimal places if you count them...
So 136,500,000 = 1.4 x 10^8 to 2 significant figures in standard form.
So with that in mind boox - what would it be to 3 SF and 4SF?
(PS - you ony need to ask the question once...)