KitSoundwave

@cryptoaops: I'm pretty sure they are. To the first question: 

add 21 to both sides and divide both sides by -4 to get x=-5

To the second question: subtract 12 on both sides and multiply both sides by 3 to get m=18

To the third question: distribute and subtract 10 on both sides and divide both sides by -12 to get z=-4

To the last question: combine like terms and add the numbers and add 5 to both sides and divide both sides by 7 to get a=5

sniped -_-

in this case the formula would be what Joe owes subtracted by how many dollars Joe paid Mike, so 49-23=26

also @cryptoaops, I'm pretty sure you know me. I'm dd0

btw, I upvoted your post. 

My answer: 

first add up all of the individiuals who has [color] hair. 

50+24+5+17=96

and they're asking how many people have blond hair and that is 24

24/96=0.25=25%

@IWantToHelp: There is an edit feature on web2.0calc. If you want to add on to you post just edit it. Instead of posting twice just edit your first post (if you want.)

The question asks: How many times does 42 go into 125? 

simply divide 125/42=2 R41 so the answer is 2

almost 3 though :)

ik cphill has a faster typing speed than me I think but here's my answer: 

The cost of each pizza is 78/6=13

the cost of each ice cream is 18/6=3

the bill is the total cost of the pizza and the ice cream they spent altogether so 78+18=96

since there are six friends and the bill is equally spit among them six, 96/6=16

Well, I'm late. But if other people is stuck on this problem and want a hint, here's one: 

the denominator (x^2+2 in this case) can't equal 0 because then it would be undefined. 

This looks like a math question, but can you please translate this into English? 

Or maybe write the equation without latex? because some latex doesn't seem to show and most latex under square roots don't show here. I tried it before. 

If @OP didn't use latex, then I guess the equation would be: f(x) = arctan(cosx)/arcsin(1-2xsqrtf'(0)