The ratio of the number of tomato plants in inessa’s garden to the number of tomato plants in ralph’s garden was 5: 6. after 1/2 the tomato plants from inessa’s garden were replanted in ralph’s garden, ralph’s garden had 850 tomato plants. how many tomato plants did ralph’s garden have in the first place?

Let "x" represent the number of units
5x = the number of tomato plants in Inessa's garden
6x = the number of tomato plants in Ralph's garden

the question says that half (1/2 x (5x)) of Inessa's tomato plants are taken from her garden and put into Ralph's garden 
this means that Ralph has a total of 850 tomato plants in his garden

using all of this information, we get the following (which we have to solve):
(1/2)(5x) + 6x = 850

when we solve for "x", we find that:
"x" = 100

so, going back to the original statement, if Ralph started out with (6x) tomato plants, and "x" = 100, we have to multiply 6 by 100

doing so gives us our final
Ralph had 600 tomato plants in the beginning

I hope this helps! :D

It is going to be the third choice