Sn=A1(1-r^n)/(1-r)
Sum of a finite geometric series formula
We know the sum, number of terms and rate, so you plug those in.
-255=A1(1-(-4)^4))/(1-(-4)
-255=A1(1-256)/5
-255=A1(-255)/5
-1275=A1(-255)
5=A1
Hope this helped! Let me know if you have any questions.
1.5 would be the answer I think
Treat it just like and equation at first. Multiply the 10 on both sides to get rid of it, leaving you with 50 
x. Then on the number line, since there is a line under it, you would make a filled in circle and an arrow pointing towards 51 and beyond
I'm pretty sure the answer is 4 because, 4*21= 84.
So 1 hour= 60 minutes
60+25= 85 minutes
Now we should subtract the 42
85-42=43
