please walk me through this I am having a hard time with this

Question

A survey of 500 showed the following
15 had only camping
20 had only hiking trails
35 had only picnicking
185 had camping
140 had camping and hiking trails
125 had camping and picnicking
210 had hiking trails
Determine the
a) number of parks that had at least one of the features
b) had all three features

Answer 1

If we label the pats of the circles in our Venn diagram,

15+CH+CP+CHP = 185
CH+CHP = 140
CP+CHP = 125
20+CH+CHP+HP = 210

from these we can see that

CH = 45
CP = 30
HP = 50
CHP = 95

a) sum of them all is 290
b) CHP = 95