Ok! So first, 2 hours are 120 minutes and 55 + 35 = 90
120 - 90 = 30
So the answer is A. Cindy spends 30 minutes on History
Hope it helps!
Answer:

Step-by-step explanation:
can be represented as
and
can be represented as
. Therefore, the expression can be rewritten as:

The rule for multiplying two exponents with the same base is you add the exponents. For example: 
We can use the same property to get:

which is just
after you add the fractions
Answer:
b. (1, 3, -2)
Step-by-step explanation:
A graphing calculator or scientific calculator can solve this system of equations for you, or you can use any of the usual methods: elimination, substitution, matrix methods, Cramer's rule.
It can also work well to try the offered choices in the given equations. Sometimes, it can work best to choose an equation other than the first one for this. The last equation here seems a good one for eliminating bad answers:
a: -1 -5(1) +2(-4) = -14 ≠ -18
b: 1 -5(3) +2(-2) = -18 . . . . potential choice
c: 3 -5(8) +2(1) = -35 ≠ -18
d: 2 -5(-3) +2(0) = 17 ≠ -18
This shows choice B as the only viable option. Further checking can be done to make sure that solution works in the other equations:
2(1) +(3) -3(-2) = 11 . . . . choice B works in equation 1
-(1) +2(3) +4(-2) = -3 . . . choice B works in equation 2
B. 24x2 is the correct answer