A textbook store sold a combined total of 331 physics and sociology textbooks in a week. The number of sociology textbooks sold was 45 less than the number of physics textbooks sold. How many textbooks of each type were sold?

Number of sociology books sold = 143 books

              Number of physics books sold = 143 + 45 = 188 books

Step-by-step explanation:

Let us take the number of sociology books sold = x

Number of physics books sold = x+45

So now we can form an equation

x+x+45 = 331

2x+45 = 331

2x = 331-45

2x = 286

x = 286 ÷ 2

x = 143

x= -3

step-by-step explanation:

step 1: simplify brackets

4 - x - 1 = 6

step 2: simpilfy

3 - x = 6

step 3: subtract 3 from both sides

-x = 6 - 3

step 4: simpilfy 6 - 3

-x = 3

step 5: multiply both sides by -1

x = -3

3. parallelogram

step-by-step explanation:

we turn each of our sides into direction vectors

ab=b-a=(3 - 7, 1 - 0) = (-4, 1)

bc=c-b=(1,6)

cd=d-c=(4,-1)

da=a-d=(-1,-6)

we see how the opposite sides have negated direction vectors; this is characteristic of a parallelogram.   we have congruent sides ab=cd and bc=da with unequal lengths because 1^2+6^2 is different from (-4)^2+1^2.   so it's not a square or a rhombus.  

we check the dot product of direction vectors of adjacent sides.   we have

ab dot bc = -4(1) + 1(6) = 2

that's not zero so the sides are not perpendicular.   we've ruled out rectangle.

the direction vectors indicate two pairs of congruent parallel sides, so we choose parallelogram over trapezoid.