Why do scientists need scientific models? a)they can often be used to make predictions. b)once established, they become fairly rigid and rarely change over time. c)they exactly present the scientific principle being demonstrated. d) they are typically based on mathematical explanations.

I think the correct answer would be the first option. Scientists need scientific models because they can often be used to make predictions. Models are representation of a process, natural phenomenon, or an idea that is being used to describe and define the occurrence which cannot be seen directly. These are very useful tools in order to predict certain values that would be tedious to be obtain through experiment. Also, this would help scientists to obtain values that is outside the range of their experiment. Examples of these models are the models of the motions of the earth, sun and the moon.

the catch is that the top numbers are atomic masses the bottom numbers are the numbers of protons and electrons in an uncharged atom. they are the number of that atoms as you would find them on the periodic table. further, the numbers on the left are used to determine the missing numbers on the right

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer