Answer: D
Step-by-step explanation:

Answer:
7x + 7
Step-by-step explanation:
2x + 5x = 7x
5 +2 = 7
heather can do 2 problems in 10 minutes....60 minutes in an hr
2/10 = x / 60...2 problems to 10 min = x problems to 60 min
10x = 120
x = 120/10
x = 12....so she can do 12 problems in 1 hr
Joel can complete 3 problems in 15 minutes...
3/15 = x / 60
15x = 180
x = 180/15
x = 12....so he can do 12 problems in 1 hr
so 24 problems can be done in 1 hr
Heather started with 3 problems done and Joel started with 2 problems done....added = 5 problems already done
and it is asking between 30 and 50 hrs.....so there is no equal sign in ur problem
ur answer is : 30 < 24x + 5 < 50 <==
While estimating you would round the decimals and you would think in terms of how would the answer look like when you multiply 64 with 10... 640ish..and then you think about the decimals a little,,, soyou will put decimal after 64... and that will give you 64.0 or something ...While the exact answer id 65.79... Close enough.
Hope I helped..
Please mark the brainliest if I did help!