Since (78-23) is in the bracket, you need to perform the operation of minus first.
that get you with
-56x(55)÷4
and then you just do it step by step
-56x55 = -3080
-3080÷4 = -770
F(x) = 20x+300
you sub in the x values (120 hours and 100 hours) for each equation
the only one they both work for is the last one
f(x) = 20x + 300
f(100) = (20 * 100) + 300 = 2000 + 300 = 2300
f(120) = (20 * 120) + 300 = 2400 + 300 = 2700
we have that
−4+8−16+32−.....
a1=-2*(-2)-----> -4
a2=-4*(-2)-----> +8
a3=+8*(-2)-----> -16
a4=-16*(-2)----> +32
a5=+32*(-2)----> -64
a6=-64*(-2)-----> +128
a7=+128*(-2)-----> -256
The sum of the first 7 terms of the series is
<span>[a1+a2+a3+a4+a5+a6+a7]-----> [-4+8-16+32-64+128-256]------->
-172</span>
<span>
the answer is -172</span>
